A mmap-window is not guaranteed to give you the whole object, but the
indexer currently assumes so.

Loop asking for more data until we've successfully CRC'd all of the
packed data.

Up to now, deltas needed to be enterily in the packfile, and we tried
to decompress then in their entirety over and over again.

Adjust the logic so we read them as they come, just as we do for full
objects. This also allows us to simplify the logic and have less
nested code. The delta resolving phase still needs to decompress the
whole object into memory, as there is not yet any streaming
delta-apply support, but it helps in speeding up the downloading
process and reduces the amount of memory allocations we need to do.

The new API allows us to read the object bit by bit from the packfile,
instead of needing it all at once in the packfile. This also allows us
to hash the object as it comes in from the network instead of having
to try to read it all and failing repeatedly for larger objects.

This is only the first step, but it already shows huge improvements
when dealing with objects over a few megabytes in size. It reduces the
memory needs in some cases, but delta objects still need to be
completely in memory and the old inefficent method is still used for
that.

This allows us to take objects from the packfile as a stream instead
of having to keep it all in memory.

Add API to calculate ahead/behind count

Fix a typo that caused a failing test, and use cl_assert_equal
instead of cl_assert.

`revwalk.h:commit_lookup()` -> `git_revwalk__commit_lookup()`
and make `git_commit_list_parse()` do real error checking that
the item in the list is an actual commit object.  Also fixed an
apparent typo in a test name.

Push! By schu, phkelley, and congyiwu

Ignore invalid entries by default

Fix git_branch_tracking() for branches with empty merge and/or remote config entries

fetch: enhance test coverage

Enhance diff test coverage between a null Tree and the Workdir

Consolidate text buffer functions

Moved it into graph.{c,h} which i created for the new "graph"
functions namespace. Also adjusted the function prototype
to use `size_t` and `const git_oid *`.

Adds a repo with a more complex topology to test the ahead-behind
count.

There are many scattered functions that look into the contents of
buffers to do various text manipulations (such as escaping or
unescaping data, calculating text stats, guessing if content is
binary, etc).  This groups all those functions together into a
new file and converts the code to use that.

This has two enhancements to existing functionality.  The old
text stats function is significantly rewritten and the BOM
detection code was extended (although largely we can't deal with
anything other than a UTF8 BOM).

Fix uninitialized variable

clang-SVN HEAD kindly provided my the info, that sm_repo maybe
uninitialized when we want to free it (If the expression in line 358 or
359/360 evaluate to true, we jump to "cleanup", where we'd use sm_repo
uninitialized).

Loads a disk alternate by path to the ODB. Mimics the
`GIT_ALTERNATE_OBJECT_DIRECTORIES` shell var.

The Great Renaming of 2012