mq: add '.' and '..' to list of forbidden patch names

When an empty string is being passed to normname
it would return '.' causing checkfile() to always
return that a patch with that name exists.

hgext/mq.py

@@ -834,7 +834,7 b' class queue(object):'
                 raise util.Abort(_("local changes found"))
         return m, a, r, d
 
-    _reserved = ('series', 'status', 'guards')
+    _reserved = ('series', 'status', 'guards', '.', '..')
     def check_reserved_name(self, name):
         if (name in self._reserved or name.startswith('.hg')
             or name.startswith('.mq') or '#' in name or ':' in name):

tests/test-mq-qnew.t

@@ -15,6 +15,8 b''
   >     hg qnew series
   >     hg qnew status
   >     hg qnew guards
+  >     hg qnew .
+  >     hg qnew ..
   >     hg qnew .hgignore
   >     hg qnew .mqfoo
   >     hg qnew 'foo#bar'
@@ -102,6 +104,8 b' plain headers'
   abort: "series" cannot be used as the name of a patch
   abort: "status" cannot be used as the name of a patch
   abort: "guards" cannot be used as the name of a patch
+  abort: "." cannot be used as the name of a patch
+  abort: ".." cannot be used as the name of a patch
   abort: ".hgignore" cannot be used as the name of a patch
   abort: ".mqfoo" cannot be used as the name of a patch
   abort: "foo#bar" cannot be used as the name of a patch
@@ -167,6 +171,8 b' hg headers'
   abort: "series" cannot be used as the name of a patch
   abort: "status" cannot be used as the name of a patch
   abort: "guards" cannot be used as the name of a patch
+  abort: "." cannot be used as the name of a patch
+  abort: ".." cannot be used as the name of a patch
   abort: ".hgignore" cannot be used as the name of a patch
   abort: ".mqfoo" cannot be used as the name of a patch
   abort: "foo#bar" cannot be used as the name of a patch