Propagate Ruby's cwd to Java via Dir.chdir

Ruby.setCurrentDirectory() is responsible for doing the work.
Ignore SecurityException for now. (Though a warning might be
appropriate.)

Fixes #971.
Maintain 1.8 compatibility in Dir.chdir spec
Revert "Maintain 1.8 compatibility in Dir.chdir spec"

This reverts commit e124632ac52f92d7dccd44e8c906673fc6993ab9.
Revert "Propagate Ruby's cwd to Java via Dir.chdir"

This reverts commit 42198651fe5ead7d14df97641588a9dbf4711e9e.

Need to fix Embedded tests.
Merge remote-tracking branch 'origin/master'