* Fetch ref (relative to $GIT_DIR/refs) from the remote, and store
* the 20-byte SHA1 in sha1. Return 0 on success, -1 on failure. To
* be provided by the particular implementation.
* Fetch ref (relative to $GIT_DIR/refs) from the remote, and store
* the 20-byte SHA1 in sha1. Return 0 on success, -1 on failure. To
* be provided by the particular implementation.