Fix issue with relative import when using single header file import.

-- The commit propagates the package option to the newly create
     module node so it is recognized by SWIG
  -- Added a relativeimport test for this combination
     (in lack of py3 I was not able to test it with py3 but it
      "should just work")

Examples/python/import_packages/relativeimport3/runme.py

@@ -0,0 +1,9 @@
+# Test import of modules content from within __init__.py
+print "Testing %module(package=...) with -relativeimport"
+import sys
+if sys.version_info < (3,0):
+  import py2.pkg2.bar
+  print "  Finished importing py2.pkg2.bar"
+else:
+  import py3.pkg2.bar
+  print "  Finished importing py3.pkg2.bar"