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 following modes:

• SHARED_UMASK - Use permissions configured by umask - the default.
• SHARED_GROUP - Use "--shared=group" behavior, chmod'ing the new repo to be group writable and "g+sx" for sticky group assignment.
• SHARED_ALL - Use "--shared=all" behavior, adding world readability.
• Anything else - Set to custom value.