Should Regexp literal be compiled in compilation phase or in execution phase?

As @mattn mentioned in issue #856, literal of regexp cannot be exported to RITE.
This patch fixes this issue, but changes the way to handle Regexp literal.

For example, 
* Regexp instance is created in execution phase.
  Therefore Regexp instance is created each time when the VM executes the code which includes Regexp literal.

I think that this patch may not be the best way to support Regexp literal, but the realistic way.