Handling of NFS4ERR_OP_NOT_IN_SESSION and NFS4ERR_NOT_ONLY_OP errors.

Operations  other than SEQUENCE, BIND_CONN_TO_SESSION, EXCHANGE_ID,
CREATE_SESSION, and DESTROY_SESSION, MUST NOT appear as the first
operation in a COMPOUND.  Such operations MUST yield the error
NFS4ERR_OP_NOT_IN_SESSION if they do appear at the start of a COMPOUND.

If any of CREATE_SESSION, EXCHANGE_ID, DESTROY_SESSION and DESTROY_CLIENTID
are sent without a preceding SEQUENCE op, then it should be the only op in the COMPOUND.
Server must enforce utf8 encoding for the compound 'tag' argument.
Compound request with an invalid 'tag' should be replied with NFS4ERR_INVAL
Fix problems in DESTROY_SESSSION and DESTROY_CLIENTID
DESTROY_SESSION can only be invoked on a connection associated with the session
DESTROY_CLIENTID on a non-existent CLIENTID should return STALE_CLIENTID