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/nonpkg.py

@@ -1,6 +1,17 @@
+import os
+import subprocess
+import sys
+
+print(" Starting subtest " + os.path.basename(__file__))
+
 # import robin as a module in the global namespace
 
 import robin
+print("  Finished importing robin")
 
 if not(robin.run() == "AWAY!"):
     raise RuntimeError("test failed")
+
+commandline = sys.executable + " -m robin"
+subprocess.check_call(commandline, shell=True)
+print("  Finished running: " + commandline)