r2599 - considerConfiguredConstraint(): move constraint handling here from trigger_i...

r2599  - considerConfiguredConstraint(): move constraint handling here from trigger_isloadbalancer(), which becomes trivial
 - trigger_ipv4(): employ considerConfiguredConstraint()
 - trigger_natv4(): idem
 - getIPv4LBList(): phased out, its code merged into getNarrowObjectList()
 - getNarrowObjectList(): expect constraint name instead of type list
 - IPV4LB_LISTSRC: adjusted default value
 - NAMEFUL_OBJTYPES: replaced with NAMEWARN_LISTSRC
 - REQUIRE_ASSET_TAG_FOR: replaced with ASSETWARN_LISTSRC
 - IPV4_PERFORMERS: replaced with IPV4OBJ_LISTSRC
 - NATV4_PERFORMERS: replaced with IPV4NAT_LISTSRC