Overriding join() in PDBPersistentHashMap.
Merge branch 'master' into persistentmap-join
Merge branch 'persistentmap-join'. Fixes cwi-swat/rascal#714.
Merge branch 'master' into new-specialized-trie-layout

Conflicts:
	src/org/eclipse/imp/pdb/facts/util/TrieSetGPCE0To4.java