With the isolation of complex reads, we can now try to refresh the
on-disk file before reading a value from it.

This changes the semantics a bit, as before we could be sure that a
string we got from the configuration was valid until we wrote or
refreshed. This is no longer the case, as a read can also invalidate the
pointer.

When writing out, parse the resulting file instead of adding or
replacing the value locally. This has the effect of reading external
changes as well.

This will be used by the writing commands in a later step.

Current code sets the active map to a new one and builds it whilst it's
active. This is a race condition with someone else trying to access the
same config.

Instead, let's build up our new map and swap the active and new one.

This way we can assume we have a consistent view of the config situation
when we're looking up remote, branch, pack-objects, etc.

In order to have consistent views of the config files for remotes,
submodules et al. and a configuration that represents what is currently
stored on-disk, we need a way to provide a view of the configuration
that does not change.

The goal here is to provide the snapshotting part by creating a
read-only copy of the state of the configuration at a particular point
in time, which does not change when a repository's main config changes.

On set, we set/add the value written to the config's internal values,
but we do not refresh old values.

Document this in a test in preparation for the refresh changes.

Make index iterator thread safe

We treat this as a NUL-terminated string, so make sure that we add the
terminator.

The checks to see if files were out of date in the attibute cache
was wrong because the cache-breaker data wasn't getting stored
correctly.  Additionally, when the cache-breaker triggered, the
old file data was being leaked.

I don't love this approach, but achieving thread-safety for
attribute and ignore data while reloading files would require a
larger rewrite in order to avoid this.  If an attribute or ignore
file is out of date, this holds a lock on the file while we are
reloading the data so that another thread won't try to reload the
data at the same time.

In the threading tests, I was still seeing a race condition where
the same item could end up being inserted multiple times into the
index.  Preserving the sorted-ness of the index outside of the
`index_insert` call fixes the issue.

This is a big refactoring of the attribute file cache to be a bit
simpler which in turn makes it easier to enforce a lock around any
updates to the cache so that it can be used in a threaded env.
Tons of changes to the attributes and ignores code.

While I was looking at the conflict cleanup code, I looked over at
the tree cache code, since we clear the tree cache for each entry
that gets removed and there is some redundancy there.  I made some
small tweaks to avoid extra calls to strchr and strlen in a few
circumstances.

I introduced a leak into conflict cleanup by removing items from
inside the git_vector_remove_matching call.  This simplifies the
code to just use one common way for the two conflict cleanup APIs.

When an index has an active snapshot, removing an item can cause
an error (inserting into the deferred deletion vector), so I made
the git_index_conflict_cleanup API return an error code.  I felt
like this wasn't so bad since it is just like the other APIs.

I fixed up a couple of comments while I was changing the header.

The iterator pushes and pops ignores incrementally onto a list as
it traverses the directory structure so that it doesn't have to
constantly recheck which ignore files apply.  With the new ref
counting, it wasn't decrementing the refcount on the ignores that
it removed from the vector.

Some ignore files were not being freed from the cache.

Clear up some of the various "find" functions and the snapshot
API naming to be things I like more.

This makes the lock management on the index a little bit broader,
having a number of routines hold the lock across looking up the
item to be modified and actually making the modification.  Still
not true thread safety, but more pure index modifications are now
safe which allows the simple cases (such as starting up a diff
while index modifications are underway) safe enough to get the
snapshot without hitting allocation problems.

As part of this, I simplified the allocation of index entries to
use a flex array and just put the path at the end of the index
entry.  This makes every entry self-contained and makes it a
little easier to feel sure that pointers to strings aren't
being accidentally copied and freed while other references are
still being held.

This adds a basic test of doing simultaneous diffs on multiple
threads and adds basic locking for the attr file cache because
that was the immediate problem that arose from these tests.

This makes the index iterator honor the GIT_ITERATOR_IGNORE_CASE
and GIT_ITERATOR_DONT_IGNORE_CASE flags without modifying the
index data itself.  To take advantage of this, I had to export a
number of the internal index entry comparison functions.  I also
wrote some new tests to exercise the capability.

This surrounds any function that mutates the entries vector with
a mutex so it can be safely snapshotted.

The usefulness of these helpers came up for me while debugging
some of the iterator changes that I was making, so since they
have also been requested (albeit indirectly) I thought I'd include
them.

Again, laying groundwork for some index iterator changes, this
contains a bunch of code refactorings for index internals that
should make it easier down the line to add locking around index
modifications.  Also this removes the redundant prefix_position
function and fixes some potential memory leaks.

This is just laying some groundwork for internal index changes
that I'm working on.

Support for format-patch

Add GIT_BRANCH_LOCAL_AND_REMOTE to git_branch_t enum

git_branch_t is an enum so requesting GIT_BRANCH_LOCAL | GIT_BRANCH_REMOTE is not possible as it is not a member of the enum (at least VS2013 C++ complains about it).

This fixes a regression introduced in commit a667ca82 (PR #1946).

Signed-off-by: Sven Strickroth <email@cs-ware.de>

Fix core.excludesfile named .gitignore

Add cherry pick support

It will form part of the subject line and should thus be one line.

Introduce git_diff_get_stats, git_diff_stats_files_changed, git_diff_stats_insertions, git_diff_stats_deletions and git_diff_stats_to_buf