Forbid re-adding dropped counter columns

patch by Aleksey Yeschenko; reviewed by Jonathan Ellis for
CASSANDRA-7831
Merge branch 'cassandra-2.0' into cassandra-2.1.0

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Update version number for 2.1.0-rc7
Better err msg when condition is set on PK column

Patch by Tyler Hobbs; review by Sylvain Lebresne for CASSANDRA-7804
Merge branch 'cassandra-2.0' into cassandra-2.1.0
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/cql3/statements/ModificationStatement.java
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Ninja: fix bad merge of CASSANDRA-7804
proleptic calendar, logging changes, tweaking exception messages
Merge branch 'cassandra-2.1' of https://github.com/apache/cassandra into 7523_211
remove NanoTime, switch Time to Long based, expand Date to support -Int to Int