~/.tmux.conf: Fix tmux config

It was not read by tmux because it contained errors after not having
updated it for ages.  Now it should be better.  I don't think I want to
keep the rest, but will see.

.tmux.conf

# [stolen tmux.conf]: https://gist.github.com/1689941#file_.tmux.conf
# [patched fonts]: https://github.com/Lokaltog/vim-powerline/wiki/Patched-fonts
set -g mode-mouse on
set -g mouse on
set -g default-terminal "screen-256color"
set -g status-utf8 on
set-option -g set-titles on
set-option -g set-titles-string "tmux(#I): #W #T"
set-option -g history-limit 10000