Ignore EPIPE in pipefilter

This hides the following traceback (there's a race condition involved,
so you may have to try a few times to hit it):

$ hg sign --key key-that-does-not-exist
Signing 2062:4bad92f4ea65
gpg: skipped "key-that-does-not-exist": secret key not available
gpg: signing failed: secret key not available
Exception in thread Thread-1:
Traceback (most recent call last):
  File "threading.py", line 442, in __bootstrap
    self.run()
  File "threading.py", line 422, in run
    self.__target(*self.__args, **self.__kwargs)
  File "mercurial/util.py", line 24, in writer
    pin.close()
IOError: [Errno 32] Broken pipe

abort: Error while signing

mercurial/util.py

@@ -20,8 +20,12 b' def pipefilter(s, cmd):'
     '''filter string S through command CMD, returning its output'''
     (pout, pin) = popen2.popen2(cmd, -1, 'b')
     def writer():
+        try:
         pin.write(s)
         pin.close()
+        except IOError, inst:
+            if inst.errno != errno.EPIPE:
+                raise
 
     # we should use select instead on UNIX, but this will work on most
     # systems, including Windows