Merge branch 'python-obfuscated-import-errors'

* python-obfuscated-import-errors:
  More Python module loading simplification
  Simpler Python module loading
  The Python module import logic has changed to stop obfuscating real ImportError problems.

Examples/python/import_packages/split_modules/README

@@ -2,6 +2,9 @@
 between two packages.  Specifically the pure python part is part of a package
 and the C/C++ part is not in any package at all.  Historically SWIG has
 supported this sort of thing.
+From SWIG 4.0.0 onwards, split modules are not supported by default.
+The %module directive needs to be customised with the moduleimport attribute
+in order to import the a global C/C++ module.
 
 vanilla        # "plane Jane" module both halves in pkg1
 vanilla_split  # python 1/2 in pkg1 C 1/2 in global namespace

Examples/python/import_packages/split_modules/vanilla_split/foo.i

@@ -1,4 +1,9 @@
-%module(package="pkg1") foo
+#if defined(SWIGPYTHON_BUILTIN) /* defined when using -builtin */
+%module(package="pkg1", moduleimport="from $module import *") foo
+#else
+%module(package="pkg1", moduleimport="import $module") foo
+#endif
+
 %{
 static unsigned count(void)
 {