Disable ClassCache of JITed code when invokedynamic is enabled.
*Only* encode Java Strings as UTF-16 if that's default internal.
Patch around JI specs that break with new Java 8 collections.

Specifically, Java 8 adds #sort to List (sorts in place given a
comparator, so our zero-arg calls and return value expectations
fail), #replace to Map (replaces a given key with a given value),
and #merge to Map (merges a given key's value with an incoming
value). This causes our monkey-patched versions to not be visible
and a few specs to break.
Remove sketchy test for concurrent require.

This behavior is also be covered by tests in MRI's suite and
RubySpec, and those do not appear to be quite as flaky in CI.
None of these tests are particularly reliable, but ours appers to
be a bit worse than the others.
Merge branch 'jruby-1_7'

Conflicts:
	spec/java_integration/types/map_spec.rb