vim-patch:7.4.423

Problem:    expand("$shell") does not work as documented.
Solution:   Do not escape the $ when expanding environment variables.

https://code.google.com/p/vim/source/detail?r=v7-4-423
Update busted to 2.0.rc4.
Merge pull request #1702 from fwalch/update-busted

Update busted to 2.0.rc4.
Merge pull request #1701 from fwalch/vim-7.4.423

vim-patch:7.4.423