Custom Python module importing code

Add optional moduleimport attribute to %module so that the
default module import code can be overridden. See the
"Searching for the wrapper module" documentation in Python.html.
Example:

  %module(moduleimport="import _foo") foo

$module also expands to the low-level C/C++ module name, so
the following is the same as above

  %module(moduleimport="import $module") foo

Issue https://github.com/swig/swig/issues/769

Examples/test-suite/python/Makefile.in

@@ -63,6 +63,7 @@ CPP_TEST_CASES += \
 	python_director \
 	python_docstring \
 	python_extranative \
+	python_moduleimport \
 	python_nondynamic \
 	python_overload_simple_cast \
 	python_pickle \