[ebxml-msg] Schema problem, errorCode values missing

In the latest Schema, I notice that the syncReply attribute has a default
use, which appears to be "required", but the Message Service spec indicates
that this attribute is OPTIONAL. (line 918).

Also, as a nit, there are two mentioned errorCodes which are not included
in the summary on page 32, "NotRecognized" (line 837), and "MimeProblem"
(lines 1019 & 1022).

Bob