use external index locking
Merge branch 'mjmh' of https://github.com/triAGENS/ArangoDB into mjmh
fixed startup race conditions
fixed some unique constraint violation handling
Merge branch 'mjmh' of https://github.com/triAGENS/ArangoDB into mjmh

Conflicts:
	arangod/VocBase/document-collection.cpp
	arangod/Wal/DocumentOperation.h