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/test-lib.sh

@@ -63,6 +63,8 @@ do
 		exit 0 ;;
 	-v|--v|--ve|--ver|--verb|--verbo|--verbos|--verbose)
 		verbose=t; shift ;;
+	--no-python)
+		no_python=t; shift ;;
 	*)
 		break ;;
 	esac