Fix aggregation fn on empty selection, column names

Patch by Benjamin Lerer; reviewed by Tyler Hobbs for CASSANDRA-8229
Fix ordering on SSTableScanner / SSTableReader close

Patch by jmckenzie; reviewed by marcuse for CASSANDRA-8019
Merge branch 'cassandra-2.1' into trunk
Fix incremental repair not remove parent session on remote

patch by yukim; reveiwed by krummas for CASSANDRA-8291
Merge branch 'cassandra-2.1' into trunk

Conflicts:
	src/java/org/apache/cassandra/service/ActiveRepairService.java
Wait for all repair sessions to finish

patch by yukim; reviewed by krummas for CASSANDRA-8208
add check of the system wall clock time at startup

patch by jasobrown; reviewed by driftx for CASSANDRA-8305
Merge branch 'cassandra-2.1' into trunk
Add more logging to be able to debug what files readMeter can be null for.

Patch by marcuse; reviewed by thobbs for CASSANDRA-8238
Merge branch 'cassandra-2.1' into trunk
Do more aggressive ttl expiration checks to be able to drop more sstables

Patch by Bjorn Hegerfors; reviewed by marcuse and slebresne for CASSANDRA-8243
Merge branch 'cassandra-2.1' into trunk

Conflicts:
	test/unit/org/apache/cassandra/db/compaction/TTLExpiryTest.java
Deal with conflicts between system functions and UDFs

patch by Robert Stupp; reviewed by Benjamin Lerer for CASSANDRA-7813
Allow snapshot-based repair on Windows for 3.0

Patch by jmckenzie; reviewed by yukim for CASSANDRA-8309
Remove post-2.1 dead schema migrations and columns
Fix CFMetaData compaction-related warnings
Merge branch 'cassandra-2.1' into trunk
fix test throw unknown keyspace error
don't declare throwing exceptions that aren't
remove dead field