'Decrement the value of C{key} by given value (default to 1).
C{key} must be consistent with an int. Return the new value, coerced to
0 if negative.
@param key: the key to modify.
@type key: L{bytes}
@param val: the value to decrement.
@type val: L{int}
@return: a deferred with will be called back with the new value
associated with the key (after the decrement).
@rtype: L{Deferred}'

def decrement(self, key, val=1):

    return self._incrdecr('decr', key, val)
