add is_write_type method for merge query
add is_write_type method for merge query

Signed-off-by: tetsuro yoshikawa <b8670bc07dd7d14958f72029c0a799584320cbd7@gmail.com>

Tpojka/CodeIgniter,ytetsuro/CodeIgniter,butane/CodeIgniter,tianhe1986/CodeIgniter,madwings/InsaneDB,madwings/InsaneDB,poing/CodeIgniter,madwings/InsaneDB,poing/CodeIgniter,tianhe1986/CodeIgniter,ganiutomo/CodeIgniter,ganiutomo/CodeIgniter,ytetsuro/CodeIgniter,bcit-ci/CodeIgniter,bcit-ci/CodeIgniter,smallp/CodeIgniter,madwings/InsaneDB,tianhe1986/CodeIgniter,tianhe1986/CodeIgniter,jim-parry/CodeIgniter,ytetsuro/CodeIgniter,Tpojka/CodeIgniter,bcit-ci/CodeIgniter,bcit-ci/CodeIgniter,smallp/CodeIgniter,tianhe1986/CodeIgniter,jim-parry/CodeIgniter,kamaslau/BasicCodeIgniter,Tpojka/CodeIgniter,asmdigital/CodeIgniter,asmdigital/CodeIgniter,Tpojka/CodeIgniter,ytetsuro/CodeIgniter,kamaslau/BasicCodeIgniter,butane/CodeIgniter,ganiutomo/CodeIgniter,kamaslau/BasicCodeIgniter,madwings/InsaneDB,jim-parry/CodeIgniter,jim-parry/CodeIgniter,asmdigital/CodeIgniter,bcit-ci/CodeIgniter,butane/CodeIgniter,Tpojka/CodeIgniter,poing/CodeIgniter,ganiutomo/CodeIgniter,poing/CodeIgniter,ganiutomo/CodeIgniter,ytetsuro/CodeIgniter,asmdigital/CodeIgniter,butane/CodeIgniter,jim-parry/CodeIgniter,asmdigital/CodeIgniter,poing/CodeIgniter,kamaslau/BasicCodeIgniter,butane/CodeIgniter