Postpone the setting of c->sru_mode until after leading options from

Postpone the setting of c->sru_mode until after leading options from
host string have been applied.  This means that host strings like the
following now work correctly in specifying the use of SRU or SRW
respectively:
	sru=get,http:z3950.loc.gov:7090/Voyager
	sru=soap,http:z3950.loc.gov:7090/Voyager
(Previously, these options were set too late to have any effect.)