Optionally work without python

In some setups (notably server setups) you do not need that dependency.
Gracefully handle the absence of python when NO_PYTHON is defined.

Signed-off-by: Johannes E. Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

t/t0000-basic.sh

@@ -42,7 +42,7 @@ fi
 
 . ./test-lib.sh
 
-"$PYTHON" -c 'import subprocess' || {
+test "$no_python" || "$PYTHON" -c 'import subprocess' || {
 	echo >&2 'Your python seem to lack "subprocess" module.
 Please check INSTALL document.'
 	exit 1