import-checker: allow *.pyd based stdlib modules

These are Windows dlls, and eliminate the following import check diffs that are
not on Unix:

  mercurial/changegroup.py mixed imports
     stdlib:    os, struct, tempfile, zlib
     relative:  bz2
  mercurial/encoding.py mixed imports
     stdlib:    locale, os
     relative:  unicodedata

contrib/import-checker.py

@@ -90,7 +90,8 b' def list_stdlib_modules():'
             for name in files:
                 if name == '__init__.py':
                     continue
-                if not (name.endswith('.py') or name.endswith('.so')):
+                if not (name.endswith('.py') or name.endswith('.so')
+                        or name.endswith('.pyd')):
                     continue
                 full_path = os.path.join(top, name)
                 if 'site-packages' in full_path: