import-checker: allow 'from typing import ...'

Suppresses the following error in test-check-module-imports.t:

  mercurial/encoding.py:24: relative import of stdlib module

contrib/import-checker.py

@@ -535,6 +535,8 b' def verify_modern_convention(module, roo'
             if fullname != '__future__':
                 if not fullname or (
                     fullname in stdlib_modules
+                    # allow standard 'from typing import ...' style
+                    and fullname != 'typing'
                     and fullname not in localmods
                     and fullname + '.__init__' not in localmods
                 ):