vim: Preliminary Python 3 support

Summary: Do not build with both Python 2 & 3.

* Avoid dynamic Python bindings.
* Support external Framework Python.
* Change vim's compiled author.
* Remove ambiguous option.

If you have problem, such as window disappear, try `[m]vim --noplugin` first.
Tested with stable, devel and head.
Reference: <http://vimdoc.sourceforge.net/htmldoc/if_pyth.html#python3>