BF: make some test directories into packages

A couple of missing __init__.py files.
RF: add setup_helpers.py to MANIFEST.in
Merge pull request #529 from matthew-brett/little-releasey-fixes

MRG: a couple of small cleanup fixes
BF: work round ugly MSVC manifest bug

Link a shared library rather than an executable to avoid nasty Windows
MSVC 10+ bug (http://bugs.python.org/issue4431).
Merge pull request #530 from matthew-brett/check-linking-with-lib

Great! thanks!