demandimport: handling new relative imports

Mercurial does not work on python2.6 because __import__ takes an
additional argument called level.  This patch merely calls the
built-in __import__ when level is passed.

mercurial/demandimport.py

@@ -77,7 +77,7 b' class _demandmod(object):'
         self._load()
         setattr(self._module, attr, val)
 
-def _demandimport(name, globals=None, locals=None, fromlist=None):
+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)
@@ -95,6 +95,9 b' def _demandimport(name, globals=None, lo'
                 return locals[base]
         return _demandmod(name, globals, locals)
     else:
+        if level is not None:
+            # from . import b,c,d or from .a import b,c,d
+            return _origimport(name, globals, locals, fromlist, level)
         # from a import b,c,d
         mod = _origimport(name, globals, locals)
         # recurse down the module chain