Fixed MacVim Python linking and added a test

Fixed MacVim that was only linking itself only to the included Python
version in OSX.
Added a test that checks if Macvim was linked to the first Python
available in $PATH
Added test for vim Python linking

Added a test that checks if vim was linked to the Python version in
first in $PATH
Check if built with Python support before testing

Before executing the test check if Vim/Macvim was built with python
support
macvim: add 7.4-73 bottle.
vim: add 7.4.430 bottle.