If plain strcmp is used, as this code did before, the final sorting may
end up different from what git-add would do (for example, 'boost'
appearing before 'boost-build.jam', because Git sorts as if it were
spelled 'boost/').

If the sorting is incorrect like this, Git 1.7.4 insists that unmodified
files have been modified.  For example, my test repository has these
four entries:

drwxr-xr-x  199 johnw  wheel   6766 Feb  2 17:21 boost
-rw-r--r--    1 johnw  wheel    849 Feb  2 17:22 boost-build.jam
-rw-r--r--    1 johnw  wheel    989 Feb  2 17:21 boost.css
-rw-r--r--    1 johnw  wheel   6308 Feb  2 17:21 boost.png

Here is the output from git-ls-tree for these files, in a commit tree
created using git-add and git-commit:

100644 blob 8b8775433aef73e9e12609610ae2e35cf1e7ec2c    boost-build.jam
100644 blob 986c4050fa96d825a1311c8e871cdcc9a3e0d2c3    boost.css
100644 blob b4d51fcd5c9149fd77f5ca6ed2b6b1b70e8fe24f    boost.png
040000 tree 46537eeaa4d577010f19b1c9e940cae9a670ff5c    boost

Here is the output for the same commit produced using libgit2:

040000 tree c27c0fd1436f28a6ba99acd0a6c17d178ed58288	boost
100644 blob 8b8775433aef73e9e12609610ae2e35cf1e7ec2c	boost-build.jam
100644 blob 986c4050fa96d825a1311c8e871cdcc9a3e0d2c3	boost.css
100644 blob b4d51fcd5c9149fd77f5ca6ed2b6b1b70e8fe24f	boost.png

Due to this reordering, git-status claims the three blobs are always
modified, no matter what I do using git-read-tree or git-reset or
git-checkout to update the index.