Add map.{foldl,foldr}5/12.

Add missing (mdi, muo) and semidet modes for map.foldl4 (foldr4 already has
them).

Strip unnecessary module qualification from the interface of the tree234 module
as per the current coding standard.

library/map.m:
	Add the above predicates.

	Add missing modes for map.foldl4/10.

library/tree234.m:
	Implement foldl5/12 and foldr5/12.

	Add missing modes for tree234.foldl4/10.

	Strip unnecessary module qualification.

NEWS:
	Announce the above additions.