Make ui.prompt repeat on "unrecognized response" again (issue897)

(this was accidentally changed in ca0d02222d6a)

mercurial/ui.py

@@ -407,6 +407,7 b' class ui(object):'
 
     def prompt(self, msg, pat=None, default="y", matchflags=0):
         if not self.interactive: return default
+        while True:
         try:
             r = self._readline(msg + ' ')
             if not pat or re.match(pat, r, matchflags):