Quick and dirty find-definitions-for-emacs

*Very* usefull slime's feature M-. -- jump to source definition for a symbol

Since swank:find-definitions-for-emacs returns a list of file locations I decided to create temporary tags file on the fly and use vim's builtin :tag command. Easy and convenient.

Dirty stuff. Hardcoded ~/tmp_tags for temporary tags file (and accordingly :set tags=~/tmp_tags in my .vimrc).
I did not try to polish the patch, since I've never used python or vimscript and I don't know what is good style.
The change is short, maybe you can turn it into a *proper* fix.

Signed-off-by: vi <ilya.vazhev@gmail.com>