Add back pandac.extension_native_helpers for compatibility

direct/src/p3d/panda3d.pdef

@@ -56,6 +56,9 @@ class panda3d(package):
            'direct.stdpy.*',
            'direct.task.*')
 
+    # Keep these modules for backward compatibility.
+    module('pandac.PandaModules', 'pandac.extension_native_helpers')
+
     module('panda3d.core',
            'panda3d.direct',
            'panda3d.fx',

makepanda/makepanda.py

@@ -2750,8 +2750,14 @@ except ImportError as err:
     if "No module named %s" not in str(err):
         raise""" % (module, module)
 
+exthelpers_code = """
+"This module is deprecated.  Import from direct.extensions_native.extension_native_helpers instead."
+from direct.extensions_native.extension_native_helpers import *
+"""
+
 if not PkgSkip("PYTHON"):
     ConditionalWriteFile(GetOutputDir() + '/pandac/PandaModules.py', panda_modules_code)
+    ConditionalWriteFile(GetOutputDir() + '/pandac/extension_native_helpers.py', exthelpers_code)
     ConditionalWriteFile(GetOutputDir() + '/pandac/__init__.py', '')
 
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