dispatch: also pass level argument to __import__ for ignored modules

I wanted to check if mercurial.demandimport could speed up the loading of
PyObjC, and ran into this: the level argument for __import__, available in
Python 2.5 and later, is silently dropped when doing an 'import *'. I have no
idea what these arguments mean, but this minor change made it work.

(Oh, and because of that 'from ... import *', PyObjC still took about 2s...)

mercurial/demandimport.py

@@ -81,7 +81,10 b' class _demandmod(object):'
 def _demandimport(name, globals=None, locals=None, fromlist=None, level=None):
     if not locals or name in ignore or fromlist == ('*',):
         # these cases we can't really delay
-        return _origimport(name, globals, locals, fromlist)
+        if level is None:
+            return _origimport(name, globals, locals, fromlist)
+        else:
+            return _origimport(name, globals, locals, fromlist, level)
     elif not fromlist:
         # import a [as b]
         if '.' in name: # a.b