Support negative timestamps in DateType.fromString

patch by slebresne; reviewed by iamaleksey for CASSANDRA-6718
Merge branch 'cassandra-1.2' into cassandra-2.0
Don't attempt cross-dc forwarding interface/mixed-version cluster with 1.1
patch by Jeremiah Jordan; reviewed by jbellis for CASSANDRA-6732
Merge branch 'cassandra-1.2' into cassandra-2.0
Use correct partitioner in AbstractViewSSTableFinder
patch by jbellis; reviewed by yukim for CASSANDRA-6734
merge from 2.0