shell/tmux: don't install/run plugins in server mode

shell/tmux/.tmux.conf

@@ -253,4 +253,4 @@ set -g @prefix_highlight_fg colour0
 set -g @prefix_highlight_output_suffix ' #[bg=default] '
 
 # Start plugin manager
-run '~/.tmux/plugins/tpm/tpm'
+if '[ -x ~/.tmux/plugins/tpm/tpm ]' 'run ~/.tmux/plugins/tpm/tpm'

shell/tmux/install

@@ -13,8 +13,10 @@ case $OSTYPE in
         ;;
 esac
 
+if [[ -z $SERVER ]]; then
     git-repo() { [[ -d $2 ]] || git clone "https://github.com/$1" "$2"; }
 
     CWD="$(dirname $0)"
     git-repo tmux-plugins/tpm "$CWD/.tmux/plugins/tpm"
     git-repo jimeh/tmuxifier "$CWD/.tmuxifier"
+fi