Optimization in collections API

[Robert Stupp]

Hello,

many real business applications make intensive use of the collections api. I have spend some time and tried to improve it a bit:
I've added a shared empty array instances to java.util.Arrays and use Arrays.EMPTY_OBJECT_ARRAY where appropriate in collection classes and reduce use of new java.util.Iterator instances where possible

The changes pass the existing tests in openjdk8 build (make test).

Robert