Feature request #1756: Add in-Vim automated tests

This came up on the vim_use mailing list in this thread. Plenty of interesting links in there:

• http://groups.google.com/group/vim_dev/browse_frm/thread/2d9463e7b167ce23/ca5ae493f061a8af
• http://code.google.com/p/lh-vim/wiki/UT
• https://github.com/dsummersl/vimunit
• http://www.vim.org/scripts/script.php?script_id=2565
• http://www.vim.org/scripts/script.php?script_id=2213
• https://github.com/tomtom/spec_vim
• http://www.vim.org/scripts/script.php?script_id=1489
• http://bitbucket.org/sjl/gundo.vim/src/tip/tests/