Changes

Clone Capabilities on input, providing a local copy when requested.  This eliminates the cloning that was occuring for each swap buffer call.

This is the first step in implementing immutable Capabilities.

Implement CapabilitiesImmutable to indicate that getRequestedCapabilities() and getChosenCapabilities() return immutable instances.  Add cloneCapabilities() to create a mutable clone of an immutable set of capabilities.

NEWT X11Display: ignore null Display handle at dispatch

Finishing Immutable changes including GLCapabiltiesImmutable.