Implemented command update0 in YAZ client which is equivalent to

Implemented command update0 in YAZ client which is equivalent to
update but uses old of Ext Update ASN.1.
Use OID 1.2.840.10003.15.1000.81.1 for privately defined charsets
in charset negotiation. Added VAL_ID_CHARSET in oid.h.
Previously no OID was used for this info.