add missing null-value omission logic (fixes #1019)
Merge remote-tracking branch 'upstream/master' into issue-1019
fix test for #1019 - it now verifies that when a MapStore's loadAllKeys() impl returns keys that are not included in the map returned by its loadAll() impl, null values (for the extra keys) don't end up in an IMap backed by that MapStore
Merge remote-tracking branch 'origin/master'

Conflicts:
	hazelcast/src/test/java/com/hazelcast/map/mapstore/MapStoreTest.java