Don't redefine powerline theme functions

In the case where a powerline theme is enabled in bash-it,
it seems prudent to avoid touching any of these functions.

plugins/available/powerline.plugin.bash

@@ -5,6 +5,13 @@ about-plugin 'enables powerline daemon'
 
 command -v powerline-daemon &>/dev/null || return
 powerline-daemon -q
+
+#the following should not be executed if bashit powerline themes in use
+case "$BASH_IT_THEME" in
+	*powerline*)
+		return
+		;;
+esac
 POWERLINE_BASH_CONTINUATION=1
 POWERLINE_BASH_SELECT=1
 bashPowerlineInit=$(python -c \