Added new member 'query_charset' for bend_initrequest structure. A

Added new member 'query_charset' for bend_initrequest structure. A
backend init handler should set this member to its native character set
for query terms. When defined, the frontend server logic will announce
this character set to a client if the negotiationModel bit is set by the
client. ALL server implementors are encouraged to specify this. If they
don't, a warning is issued.