This commit reinstates some changes to git_diff__paired_foreach
that were discarded during the rebase (because the diff_output.c
file had gone away), and also adjusts the case insensitively
logic slightly to hopefully deal with either mismatched icase
diffs and other case insensitivity scenarios.

This makes diff more careful about picking the canonical path
when generating a delta so that it won't accidentally pick up a
case-mismatched path on a case-insensitive file system.  This
should make sure we use the "most accurate" case correct version
of the path (i.e. from the tree if possible, or the index if
need be).

The exclude submodules flag was not doing the right thing, in
that a file with no diff between the head and the index and just
a delete in the workdir could be excluded if submodules were
excluded.

This simplifies some documentation and hopefully makes a couple
of things easier to read.  Also, this rearrages the order in this
branch so that the overall diff against the trunk will hopefully
be a bit cleaner.

ref: free the last ref when cancelling git_branch_foreach()

Also fixed an assert typo on nulltoken's HEAD

Memzero stuffs

On Linux: fix a warning message related to the volatile qualifier (cast)
On Windows: use SecureZeroMemory()

On both, inline the call, so that no entry point can lead back to this "secure" memory zeroing.

Fix/build warnings

cmake: Add option to specify the name of the binary

This reverts commit 095bfd74.

Fix Windows warnings and missing prototypes

This fixes problems with missing function prototypes and 64-bit
data issues on Windows.

Keep data about source of similarity

Diff code reorg plus function context in diff headers

This makes the git_diff_patch definition private to diff_patch.c
and fixes a number of other header file naming inconsistencies to
use `git_` prefixes on functions and structures that are shared
between files.

This changes the size data to uint32_t, fixes the array growth
logic to use a simple 1.5x multiplier, and uses a generic inline
function for growing the array to make the git_array_alloc API
feel more natural (i.e. it returns a pointer to the new item).

This adds two new public APIs: git_diff_patch_from_blobs and
git_diff_patch_from_blob_and_buffer, plus it refactors the code
for git_diff_blobs and git_diff_blob_to_buffer so that they code
is almost entirely shared between these APIs, and adds tests for
the new APIs.

This adds real tests for user-configured diff drivers and in the
process found a bunch of bugs.

Add high(est) config level for application specific config files

Some tools use an extra level to maintain an application specific config files on top of the normal ones. Revision 16adc9fa broke this.

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

This implements the loading of regular expression pattern lists
for diff drivers that search for function context in that way.
This also changes the way that diff drivers update options and
interface with xdiff APIs to make them a little more flexible.

signature: extend trimming to more whitespace

There are all sorts of misconfiguration in the wild. We already rely
on the signature constructor to trim SP. Extend the logic to use
`isspace` to decide whether a character should be trimmed.