def decr(self, key, delta=<NUM_LIT:1>):
return self._incrdecr("<STR_LIT>", key, delta)<EOL>
Like L{incr}, but decrements.  Unlike L{incr}, underflow is checked and
new values are capped at 0.  If server value is 1, a decrement of 2
returns 0, not -1.

@param delta: Integer amount to decrement by (should be zero or greater).
@return: New value after decrementing or None on error.
@rtype: int