Added tests for thread pool executor classes.
Added MRI 1.9.3 to Travis 'allow failure' list.
Created shared specs for thread pool executors.
Moved pending specs from thread_pool_shared to thread_pool_executor_shared.
Wrote queue specs for thread pool executors.
JavaThreadPoolExecutor now passes the new queue specs.
Implemented queue length functionality for RubyThreadPoolExecutor.
Implemented thread pool overload policies.
Merge pull request #41 from jdantonio/thread-pool-overload

Implemented thread pool overload policies.