(cqlsh) enable CTRL-R history search with libedit

patch by Aleksey Yeschenko; reviewed by Jeremiah Jordan for
CASSANDRA-7577
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.0' into cassandra-2.1.0
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk