Fix for running 'python -m' when using swig -builtin

Same as e05b5ea for -builtin.

Also added runtime tests to check 'python -m'.

Examples/python/import_packages/namespace_pkg/runme.py

@@ -1,7 +1,8 @@
 # These examples rely on namespace packages.  Don't
 # run them for old python interpreters.
-import sys
 import os.path
+import subprocess
+import sys
 
 testname = os.path.basename(os.path.dirname(os.path.abspath(__file__)))
 print "Testing " + testname + " - namespace packages"