Implement caching of authorization results

Patch by Aleksey Yeschenko; reviewed by Jonathan Ellis for
CASSANDRA-4295
Merge branch 'cassandra-1.2' into trunk

Conflicts:
	CHANGES.txt
Add support for LZ4 compression
patch by Adrien Grand; reviewed by tjake for CASSANDRA-5038
Merge branch 'cassandra-1.2' into trunk
Remove duplicate 5038 from CHANGES.txt
Add aggregate statistics to cassandra-stress
Patch by Ryan McGuire, reviewed by brandonwilliams for CASSANDRA-5243
Check for the presence of both rack and dc in the system table.
Patch by brandonwilliams, reviewed by jbellis for CASSANDRA-5211
Merge branch 'cassandra-1.2' into trunk
Fix missing columns in wide rows queries

patch by slebresne; reviewed by driftx for CASSANDRA-5225
Merge branch 'cassandra-1.2' into trunk
Make CompactionsTest.testDontPurgeAccidentaly more reliable with gcgrace=0
Simplify auth setup and make system_auth ks alterable

Patch by Aleksey Yeschenko; reviewed by Jonathan Ellis for
CASSANDRA-5112
Merge branch 'cassandra-1.2' into trunk
Avoid throwing AE when hosts don't have a hostId
Patch by brandonwilliams, reviewed by iamaleksey for CASSANDRA-5197
Merge branch 'cassandra-1.2' into trunk
fix format string specifier
Merge branch 'cassandra-1.2' into trunk
drop keyspace from user-defined compaction API; patch by yukim reviewed by jbellis for CASSANDRA-5139
Stop compactions from handing during bootstrap.
Patch by brandonwilliams, reviewed by Vijay for CASSANDRA-5244
Merge branch 'cassandra-1.2' into trunk