- fix broken compile with MSVC (does not like preprocessor #if/#else/#endif inside call to macro PyRun_String)
- enable "exectest" testcase for Python 3

Will change in 0.12

This silents GCC warnings (in 64 bits) about casting integer to pointer of different size.

cast result of "sizeof()" to "int" in testcase, silents GCC warnings about signed/unsigned comparisons