make api compatible with 5.3
make api compatible with 5.3
Merge remote-tracking branch 'origin/devel' into 2.2
issue #174: fixed key validation
do not rely that much on error message

Conflicts:
	tests/TransactionTest.php
bumped X-Arango-Version content
turn off value validation by default

this makes document creation faster
Merge branch 'master' of https://github.com/triAGENS/ArangoDB-PHP