Fixed irep index overflows, when defining new closure.

Issue #1137.
In the present implementation, when calling mrb_load_string continuously, irep is not released.
Therefore, a 16-bit index was overflowing.
Add vs2010.rake
move no block check to mrb_yield_internal
Merge pull request #1176 from h2so5/add-vs2010-toolchain

Add vs2010.rake
Merge pull request #1175 from kurodash/pr-irep-idx-overflow

Fixed irep index overflows, when defining new closure.