fix prepared statements in batch requests
Merge pull request #94 from JeremyOT/prep-batch

fix prepared statements in batch requests
Handle BoundStmts in BatchStmt.add(), unit tests
Tests for empty params in add(), related fixes
Raise exception if credentials are used with v2 protocol
Handle params=None when executing prepared stmt
Actually execute batch in integration test
Serial consistency level support
First steps towards auto paging support
Merge remote-tracking branch 'upstream/2.0' into 2.0

Conflicts:
	cassandra/decoder.py