Consider separate internal error code for MslTokenizer creation errors

[wmiaw]

MessageInputStream treats any MslEncoderException from MslEncoderFactory.createTokenizer(), MslTokenizer.more(), and the first call to MslTokenizer.nextObject() into a single internal error code of MslError.MSL_PARSE_ERROR.

It may be beneficial to separate out the tokenizer creation into a separate try/catch block to return a more specific MSL parsing error, similar to the one returned when the message data appears to be missing.