* Rework GIT_DIRREMOVAL values to GIT_RMDIR flags, allowing
combinations of flags
* Add GIT_RMDIR_EMPTY_PARENTS flag to remove parent dirs that
are left empty after removal
* Add GIT_MKDIR_VERIFY_DIR to give an error if item is a file,
not a dir (previously an EEXISTS error was ignored, even for
files) and enable this flag for git_futils_mkpath2file call
* Improve accuracy of error messages from git_futils_mkdir
This started as a complex new test for checkout going through the
"typechanges" test repository, but that revealed numerous issues
with checkout, including:
* complete failure with submodules
* failure to create blobs with exec bits
* problems when replacing a tree with a blob because the tree
"example/" sorts after the blob "example" so the delete was
being processed after the single file blob was created
This fixes most of those problems and includes a number of other
minor changes that made it easier to do that, including improving
the TYPECHANGE support in diff/status, etc.
