make JRubyClassLoader binary compatible to jruby-1.7.x again

and still keep the extra features restricted to runtime.getJRubyClassLoaders.
all other internal CL will be ClassDefiningJRubyClassLoader.
[Truffle] Remove RubyObject class - use RubyBasicObject instead in most instances.
[Truffle] Work on #object_id.
[Truffle] Wrap BigInteger up into RubyBignum - we need a place to put the ID.
[Truffle] Fix Bignum#divmod bug.
Merge commit master into truffle-head
Merge branch 'master' into truffle-head

Conflicts:
	core/src/main/java/org/jruby/truffle/nodes/control/WrapperNode.java
	core/src/main/java/org/jruby/truffle/nodes/core/BignumNodes.java
	core/src/main/java/org/jruby/truffle/nodes/core/FixnumNodes.java
	core/src/main/java/org/jruby/truffle/nodes/core/FixnumOrBignumNode.java
	core/src/main/java/org/jruby/truffle/nodes/core/FloatNodes.java
	core/src/main/java/org/jruby/truffle/nodes/core/GeneralDivModNode.java
	core/src/main/java/org/jruby/truffle/nodes/core/MathNodes.java
	core/src/main/java/org/jruby/truffle/nodes/debug/RubyWrapper.java
	core/src/main/java/org/jruby/truffle/runtime/util/RuntimeBigInteger.java