[Fix #543] Do not set tmux destroy-unattached

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Fix git-info added/deleted count formatting typo

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Merge branch 'master' of https://github.com/sorin-ionescu/prezto