procutil: use a raw string for module name

Otherwise Python 2 will coerce unicode to str.

Differential Revision: https://phab.mercurial-scm.org/D6047

mercurial/utils/procutil.py

@@ -221,7 +221,7 b' def mainfrozen():'
     """
     return (pycompat.safehasattr(sys, "frozen") or # new py2exe
             pycompat.safehasattr(sys, "importers") or # old py2exe
-            imp.is_frozen(u"__main__")) # tools/freeze
+            imp.is_frozen(r"__main__")) # tools/freeze
 
 _hgexecutable = None