git: update to v2.14

Numerous changes were made to git functions to use an object_id
structure rather than sending sha1 hashes as raw unsigned character
arrays.  The functions that affect cgit are: parse_object,
lookup_commit_reference, lookup_tag, lookup_tree, parse_tree_indirect,
diff_root_tree_sha1, diff_tree_sha1, and format_display_notes.

Commit b2141fc (config: don't include config.h by default) made it
necessary to that config.h be explicitly included when needed.

Commit 07a3d41 (grep: remove regflags from the public grep_opt API)
removed one way of specifying the ignore-case grep option.

Signed-off-by: Jeff Smith <whydoubt@gmail.com>