make it possible to specify which python interpreter should be used explicitly.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@36202 20353a03-c40f-0410-a6d1-a30d3c3de9de

buildout/Makefile

+PYTHON=python
 SOFTWARE_BUILD_PATH='/opt/erp5/'`cat VERSION.txt`
 PACKAGE_INSTALL_PATH='opt/erp5/'`cat VERSION.txt`
 ifndef $(PACKAGE_VERSION)
@@ -14,7 +15,7 @@ software: bin/buildout
 	bin/buildout
 
 bin/buildout:
-	python -S bootstrap/bootstrap.py
+	$(PYTHON) -S bootstrap/bootstrap.py
 
 # run make assert to check that all is working
 assert: bin/python2.4