cat-file: report an error on multiple --batch options

The options callback for --batch and --batch-check detects when the two mutually incompatible options are used. But it simply returns an error code to parse-options, meaning the program will quit without any kind of message to the user. Instead, let's use error() to print something and return -1. Note that this flips the error return from 1 to -1, but negative values are more idiomatic here (and parse-options treats them the same). Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>