Fix fd leak on git cmd.
Fix fd leak on git cmd.

Currently if command is called with as_proces=True, pipes for the
command will not be closed.

This change makes sure to close command file descriptors.

Conflicts:
	git/cmd.py

jeblair/GitPython,breavo/GitPython,gitpython-developers/gitpython,avinassh/GitPython,expobrain/GitPython,gitpython-developers/GitPython,avinassh/GitPython,StyXman/GitPython,expobrain/GitPython,bwrsandman/GitPython,beni55/GitPython,gitpython-developers/GitPython,ghtdak/GitPython,hvnsweeting/GitPython,h4ck3rm1k3/GitPython,bwrsandman/GitPython,zsjohny/GitPython,cdht/GitPython,manasdk/GitPython,pengshp/GitPython,roidelapluie/GitPython,pengshp/GitPython,ghtdak/GitPython,StyXman/GitPython,bwrsandman/GitPython,manasdk/GitPython,h4ck3rm1k3/GitPython,gitpython-developers/gitpython,pengshp/GitPython,beni55/GitPython,zsjohny/GitPython,hvnsweeting/GitPython,cdht/GitPython,dpursehouse/GitPython,nvie/GitPython,zsjohny/GitPython,StyXman/GitPython,avinassh/GitPython,breavo/GitPython,roidelapluie/GitPython,jeblair/GitPython,dpursehouse/GitPython,cdht/GitPython,nvie/GitPython