Remove uses of `distutils.msvc9compiler`

[dpaoliello]

distutils.msvc9compiler has been deprecated for a while, and has recently been removed, which breaks cffi on Windows.

This change:

• Removes the use of distutils.msvc9compiler.
• Removes the _remove_visual_c_ref workaround, as it's no longer required for setuputils.
• Changes test_ownlib to use the CCompiler API directly instead of manually running cl.exe.
• Fixes test failures:
  • zdistutil wasn't generating unique file names, as the first 10 characters of the test names were the same.
  • empty-test needs to export the function on Windows.

Fixes #117

[dpaoliello]

This was fixed by #118