cqlsh can't show data under python2.5, python2.6

Kris Hahn discovered a python2.6-ism in recent cqlsh changes:

        bval = escapedval.encode(output_encoding, errors='backslashreplace')

before python2.7, str.encode() didn't accept a keyword argument for the second parameter. the semantics are the same without naming the parameter, though, so removing the "errors=" bit should suffice to make it run right.

does not affect any released version, but does affect HEAD of cassandra-1.0, cassandra-1.1, and trunk.