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/py3/Makefile

@@ -0,0 +1,14 @@
+TOP        = ../../../..
+SWIG       = $(realpath $(TOP)/../preinst-swig)
+SWIGOPT    =
+LIBS       =
+
+build:
+	cd pkg2 && $(MAKE) SWIG='$(SWIG)' SWIGOPT='$(SWIGOPT)' LIBS='$(LIBS)' build
+
+static:
+	cd pkg2 && $(MAKE) SWIG='$(SWIG)' SWIGOPT='$(SWIGOPT)' LIBS='$(LIBS)' static
+
+clean:
+	$(MAKE) -f $(TOP)/Makefile SRCDIR='$(SRCDIR)' python_clean
+	cd pkg2 && $(MAKE) clean