Replace EmptyColumns with updated ArrayBackedSortedColumns

patch by Aleksey Yeschenko; reviewed by Jonathan Ellis for
CASSANDRA-6690
Don't exchange schema between nodes with different versions

patch by Aleksey Yeschenko; reviewed by Piotr Kołaczkowski for
CASSANDRA-6695
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	src/java/org/apache/cassandra/service/MigrationManager.java
Merge branch 'cassandra-2.0' into trunk
Fix stress
log at info when gossip is fine or people think it's still waiting
Merge branch 'cassandra-2.0' into trunk
SS logging 'now serving reads' is misleading
Merge branch 'cassandra-2.0' into trunk
only waitForGossip if we're configured for a multinode cluster
Merge branch 'cassandra-2.0' into trunk
turns out there's already a getLoopbackAddress
Merge branch 'cassandra-2.0' into trunk
Remove dead ColumnSlice.NavigatableMapIterator
Improvements and fixes to cassandra/stress
Patch by Benedict; reviewed by Pavel Yaskevich for CASSANDRA-6691
remove dead code
Merge branch 'cassandra-2.0' into trunk
use long math for long results
remove dead params
Avoid overlaps in LCS by not skipping levels and verifying that the candidates
don't overlap any compacting sstables.

Patch by marcuse, reviewed by jbellis for CASSANDRA-6688