ACCUMULO-2520 made GC validate data read from !METADATA table
Merge branch '1.4.5-SNAPSHOT' into 1.5.2-SNAPSHOT

Conflicts:
	server/src/main/java/org/apache/accumulo/server/gc/SimpleGarbageCollector.java
	server/src/test/java/org/apache/accumulo/server/gc/TestConfirmDeletes.java
	test/system/auto/simple/gc.py
Merge remote-tracking branch 'local14/1.5.2-SNAPSHOT' into 1.6.0-SNAPSHOT
ACCUMULO-2494 Delegate math to commons-math
Merge branch '1.5.2-SNAPSHOT' into 1.6.0-SNAPSHOT
Merge branch '1.6.0-SNAPSHOT'