Allow empty CQL3 batches as no-op

patch by slebresne; reviewed by iamaleksey for CASSANDRA-5994
Support null in CQL3 functions

patch by slebresne; reviewed by iamaleksey for CASSANDRA-5910
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	src/java/org/apache/cassandra/cql3/functions/TimeuuidFcts.java