Fix a bug in `RemovableLongSortedArraySet#retainAll()`
Split out empty-list condition for retainAll test
Fix retainAll bug

Finish the fix in #379 to deal correctly with the key domain containing Long.MAX_VALUE.
Merge pull request #380 from grouplens/hotfix/master/379-lsas-retainall

Fix bug in LSAS retainAll