Extend triggers to support CAS updates

patch by Sam Tunnicliffe; reviewed by Aleksey Yeschenko for
CASSANDRA-6882
Pick unused generations when loading new sstables

patch by Tyler Hobbs; reviewed by Jonathan Ellis for CASSANDRA-6514
Include correct consistencyLevel in LWT timeout
patch by Sankalp Kohli; reviewed by jbellis for CASSANDRA-6884
Omit tombstones from schema digests
patch by Oleg Anastasyev; reviewed by jbellis for CASSANDRA-6862
Static columns with IF NOT EXISTS don't always work as expected

patch by slebresne; reviewed by iamaleksey for CASSANDRA-6783
Extend limits.conf in debian packaging.

Patch by brandonwilliams for CASSANDRA-6104
Merge branch 'cassandra-1.2' into cassandra-2.0
Add UNLOGGED, COUNTER options to BATCH docs

patch by Tyler Hobbs; reviewed by Sylvain Lebresne for CASSANDRA-6816
Add uuid() function
patch by Carl Yeksigian; reviewed by jbellis for CASSANDRA-6473
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	CHANGES.txt