Repair shortcuts in vimfiler/vimshell

1. Replace <F12> with <c-i> to invoke "close other tabs".
2. make <c-l> work in vimfiler.
3. make <c-k>/<c-l> of normal mode in vimshell work.
4. make <c-w> in vimshell/vimfiler work. It just closes current buffer, behaves different from :BufOnly.

Signed-off-by: apporc <appleorchard2000@gmail.com>