00582bc introduced a change that required the caller of
git_blob_create_fromfile() to pass a struct stat with the stat
information for the file. Several developers pointed out that this would
make life hard for the bindings developers as struct stat isn't widely
supported by other languages.

Make git_blob_create_fromfile() stat the path itself, eliminating the
need for the file to be stat'ed by the caller. This makes
index_init_entry() more costly as the file will be stat'ed twice but
makes life easier for everyone else.