Coverity reported a memory leak in this function. However, it can only
be called once, as setup_git_directory() changes global state and hence
is not reentrant.
Mark the variable as static to indicate that this is a singleton.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>