correct handling between different tmux versions

.tmux.conf

@@ -2,6 +2,9 @@
 ### Defaults 
 ##########################################
 
+# get tmux version
+run-shell "tmux setenv -g TMUX_VERSION $(tmux -V | cut -c 6-)"
+
 # bind ctrl+a to tmux prefix 
 unbind C-b
 set -g prefix C-a
@@ -32,11 +35,10 @@ set-option -g visual-bell off
 set-option -g visual-silence off
 set-option -g bell-action none
 
-# mouse
-set -g mode-mouse on
-set -g mouse-select-pane on
-set -g mouse-resize-pane
-set -g mouse-select-window on
+# set mouse modes
+if-shell '[[ $(echo "$(tmux -V | cut -d" " -f2) >= 2.1" | bc) -eq 1 ]]' \
+	'set -g mouse on' \
+	'set -g mode-mouse on; set -g mouse-resize-pane on; set -g mouse-select-pane on; set -g mouse-select-window on'
 
 ##########################################
 ### Styling
@@ -49,7 +51,10 @@ set -g pane-active-border-bg colour236
 set -g pane-active-border-fg colour51
 
 # status line
-set -g status-utf8 on
+# UTF8 is autodetected in 2.2 onwards, but errors if explicitly set
+if-shell '[[ $(echo "$(tmux -V | cut -d" " -f2) < 2.2" | bc) -eq 1 ]]' \
+	'set -g status-utf8 on;'
+
 set -g status-justify left
 set -g status-interval 2
 set -g status-bg colour234