export MALLOC_ARENA_MAX corrrectly

Patch by brandonwilliams, reviewed by jbellis for CASSANDRA-6126
Skip strict endpoint selection for ranges if RF == nodes

Patch by Sam Tunnicliffe; reviewed by tjake for CASSANDRA-7765
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk