This minor cleanup was suggested by Johannes Schindelin.
The mmap is still fake in the sense that we don't support PROT_WRITE
or MAP_SHARED with external modification at all, but that hasn't
stopped us from using mmap() thoughout the Git code.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>