Git.pm: Avoid ppport.h

Git.pm: Avoid ppport.h

This makes us not include ppport.h which seems not to give us anything
real anyway; it is useful for checking for portability warts but since
Devel::PPPort is a portability wart itself, we shouldn't require it
for build. You can check for portability problems by calling make check
in perl/.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Junio C Hamano <junkio@cox.net>