A better timeout implementation for Safe#eval

  - now Safe#eval takes an options hash that accepts the :timeout option for seconds
  - this will wrap a super call in a custom timeout code (using the Timeout library does not work) using Threads and Thread#kill!
  - this code was 'borrowed' from javasand
  - I had to move the getCurrentScope() call to the initialization of the sandbox so the scope would persist between eval calls