Update to latest Java 8
Added stat method to FileResource and refactored RubyFileStat to make use of it.

This way RubyFileStat doesn't need to do any more custom logic for jars.
Harden against null path names.
Rewrite Ruby parts of Java exceptions raised from JI calls.

This flag was added for #1313 but not turned on. Due to continued
reports from people having trouble interpreting JI stack traces,
we have decided to do this transformation by default.

Specifying -Xrewrite.java.trace=false or
-Djruby.rewrite.java.trace=false will return to the old non-
rewriting behvaior.

See #1504 and #1313 at least. Fixes #1504.
Hmm merge instead of rebase
Appears to be working not. Fixes #1488.
Fix regression in fiber specs; check fiber queue for aliveness.
Reinstate executor thread pool for running fibers. Fixes #1443.
Avoid double-indirection for fully-synchronized locks list.
Avoid creation of null weakref on every ThreadContext.
Fix test broken by JAva stacktrace rewriting change.
Resurrect replacing '\' with '/' in JRubyFile for windows.

This should fix https://github.com/jruby/jruby/issues/1489 regression.
Merge pull request #1510 from ratnikov/fix-windows-file

Resurrect replacing '\' with '/' in JRubyFile for windows.
Minor tweaks for Fiber, Enumerator, and a fiber spec.

* Fiber yielding against a dead queue should raise before trying
  to exchange.
* Enumerator should use fiber executor.
* Fix "abandoned fibers" test to reflect new thread pooling.
Don't run fiber+exception spec on 1.8.
Checking wrong queue for shutdown handling async exception.
Silence kcode warnings in 1.9 mode.
Propagate LocalJumpError directly from fiber.
use a different verion of plexus-io for maven-jar-plugin since older versions have problems with file attributes managed by ldap [skip ci]
Update for new bytelist