py3: replace a StandardError reference

This doesn't exist on py3, and the standard way of handling this seems to be to
catch both exceptions.

hgext/fastannotate/__init__.py

@@ -155,7 +155,7 b' def _flockavailable():'
     try:
         import fcntl
         fcntl.flock
-    except StandardError:
+    except (AttributeError, ImportError):
         return False
     else:
         return True