error: Add a hint argument to RepoError

This use the same mechanism than Abort. Except clause stay distinct
because RepoError add "!" at the end of the message.

mercurial/dispatch.py

@@ -125,6 +125,8 b' def _runcatch(req):'
             commands.help_(ui, 'shortlist')
     except error.RepoError, inst:
         ui.warn(_("abort: %s!\n") % inst)
+        if inst.hint:
+            ui.warn(_("(%s)\n") % inst.hint)
     except error.ResponseError, inst:
         ui.warn(_("abort: %s") % inst.args[0])
         if not isinstance(inst.args[1], basestring):

mercurial/error.py

@@ -43,7 +43,9 b' class ParseError(Exception):'
     'Exception raised when parsing config files (msg[, pos])'
 
 class RepoError(Exception):
-    pass
+    def __init__(self, *args, **kw):
+        Exception.__init__(self, *args)
+        self.hint = kw.get('hint')
 
 class RepoLookupError(RepoError):
     pass