GIRAPH-683: Jython for Computation (nitay)
GIRAPH-694 Setting configuration in GiraphConfiguration causes
non thread safe copies (aching)
Merge remote-tracking branch 'upstream/trunk' into GIRAPH-623

Conflicts:
	giraph-core/src/main/java/org/apache/giraph/conf/AbstractConfOption.java
	giraph-core/src/main/java/org/apache/giraph/conf/GiraphConstants.java