fix problems with external module handling. found by benoit boissinot.

first fix is to not store module objects in commands.external dict,
instead use module names for key into sys.modules.  this prevents circular
reference during cleanup of aborted transaction.

second is to get name right during import of external module.

mercurial/commands.py

@@ -3371,12 +3371,12 b' external = {}'
 def findext(name):
     '''return module with given extension name'''
     try:
-        return external[name]
+        return sys.modules[external[name]]
     except KeyError:
         dotname = '.' + name
         for k, v in external.iteritems():
-            if k.endswith('.' + name) or v.__name__ == name:
-                return v
+            if k.endswith('.' + name) or v == name:
+                return sys.modules[v]
         raise KeyError(name)
     
 def dispatch(args):
@@ -3390,14 +3390,14 b' def dispatch(args):'
         sys.stderr.write(_("abort: %s\n") % inst)
         return -1
 
-    for x in u.extensions():
+    for ext_name, load_from_name in u.extensions():
         try:
-            if x[1]:
+            if load_from_name:
                 # the module will be loaded in sys.modules
                 # choose an unique name so that it doesn't
                 # conflicts with other modules
-                module_name = "hgext_%s" % x[0].replace('.', '_')
-                mod = imp.load_source(module_name, x[1])
+                module_name = "hgext_%s" % ext_name.replace('.', '_')
+                mod = imp.load_source(module_name, load_from_name)
             else:
                 def importh(name):
                     mod = __import__(name)
@@ -3406,12 +3406,10 b' def dispatch(args):'
                         mod = getattr(mod, comp)
                     return mod
                 try:
-                    name = 'hgext.' + x[0]
-                    mod = importh(name)
+                    mod = importh("hgext.%s" % ext_name)
                 except ImportError:
-                    name = x[0]
-                    mod = importh(name)
-            external[name] = mod
+                    mod = importh(ext_name)
+            external[ext_name] = mod.__name__
         except (util.SignalInterrupt, KeyboardInterrupt):
             raise
         except Exception, inst:
@@ -3419,14 +3417,15 b' def dispatch(args):'
             if u.print_exc():
                 return 1
 
-    for x in external.itervalues():
-        uisetup = getattr(x, 'uisetup', None)
+    for name in external.itervalues():
+        mod = sys.modules[name]
+        uisetup = getattr(mod, 'uisetup', None)
         if uisetup:
             uisetup(u)
-        cmdtable = getattr(x, 'cmdtable', {})
+        cmdtable = getattr(mod, 'cmdtable', {})
         for t in cmdtable:
             if t in table:
-                u.warn(_("module %s overrides %s\n") % (x.__name__, t))
+                u.warn(_("module %s overrides %s\n") % (name, t))
         table.update(cmdtable)
 
     try:
@@ -3475,9 +3474,10 b' def dispatch(args):'
                     if not repo:
                         repo = hg.repository(u, path=path)
                     u = repo.ui
-                    for x in external.itervalues():
-                        if hasattr(x, 'reposetup'):
-                            x.reposetup(u, repo)
+                    for name in external.itervalues():
+                        mod = sys.modules[name]
+                        if hasattr(mod, 'reposetup'):
+                            mod.reposetup(u, repo)
                 except hg.RepoError:
                     if cmd not in optionalrepo.split():
                         raise