This updates to the latest clar which includes the helpers
`cl_assert_equal_s` and `cl_assert_equal_i`. Convert the code
over to use those and remove the old libgit2-only helpers.
This migrates odb.c, odb_loose.c, odb_pack.c and pack.c to
the new style of error handling. Also got the unix and win32
versions of map.c. There are some minor changes to other
files but no others were completely converted.
This also contains an update to filebuf so that a zeroed out
filebuf will not think that the fd (== 0) is actually open
(and inadvertently call close() on fd 0 if cleaned up).
Lastly, this was built and tested on win32 and contains a
bunch of fixes for the win32 build which was pretty broken.
