mq: use %r to format illegal characters instead of manually quoting

This will make it easier to ban \r and \n in the next patch and still
have a sensible error message.

hgext/mq.py

@@ -1104,7 +1104,7 b' class queue(object):'
                                  % prefix)
         for c in ('#', ':'):
             if c in name:
-                raise util.Abort(_('"%s" cannot be used in the name of a patch')
+                raise util.Abort(_('%r cannot be used in the name of a patch')
                                  % c)
 
     def checkpatchname(self, name, force=False):

tests/test-mq-qnew.t

@@ -108,8 +108,8 b' plain headers'
   abort: ".." cannot be used as the name of a patch
   abort: patch name cannot begin with ".hg"
   abort: patch name cannot begin with ".mq"
-  abort: "#" cannot be used in the name of a patch
-  abort: ":" cannot be used in the name of a patch
+  abort: '#' cannot be used in the name of a patch
+  abort: ':' cannot be used in the name of a patch
   % qnew with name containing slash
   abort: path ends in directory separator: foo/ (glob)
   abort: "foo" already exists as a directory
@@ -176,8 +176,8 b' hg headers'
   abort: ".." cannot be used as the name of a patch
   abort: patch name cannot begin with ".hg"
   abort: patch name cannot begin with ".mq"
-  abort: "#" cannot be used in the name of a patch
-  abort: ":" cannot be used in the name of a patch
+  abort: '#' cannot be used in the name of a patch
+  abort: ':' cannot be used in the name of a patch
   % qnew with name containing slash
   abort: path ends in directory separator: foo/ (glob)
   abort: "foo" already exists as a directory