Mode options for git_repository_init_ext.
Set the mode field of the git_repository_init_options structure
either to the custom mode that you would like, or to one of the
defined modes.
Use permissions configured by umask - the default.
Use "--shared=group" behavior, chmod'ing the new repo to be group writable and "g+sx" for sticky group assignment.
Use "--shared=all" behavior, adding world readability.