ACCUMULO-2527 Compiler warning cleanup.

For internal use of deprecations, where applicable, new tickets with TODOs were placed in the comments to mark the
necessity to fix the code. To ease deprecation suppression, some code was lifted into a single method to reduce impact.
ACCUMULO-2531 Use VolumeConfiguration instead of instance.dfs.dir in ClientOpts

VolumeConfiguration encompasses both instance.dfs.dir and instance.volumes.
ACCUMULO-2487 match Value implementation to javadocs. check for null args.
ACCUMULO-2534 added license headers
ACCUMULO-2487 eliminate warnings about unused vars
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
ACCUMULO-2534 added license headers
Merge branch '1.4.5-SNAPSHOT' into 1.5.2-SNAPSHOT
Merge branch '1.5.2-SNAPSHOT' into 1.6.0-SNAPSHOT
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