Add LP_DEBUG_TIME for bash: if 1 shows PS1 build time

Doesn't work on zsh: looks like 'time' doesn't output anything if
applied to a shell function. Need a zsh expert.

liquidprompt

@@ -295,6 +295,8 @@ _lp_source_config()
     LP_COLORMAP_8=${LP_COLORMAP_8:-$CRIT_RED}
     LP_COLORMAP_9=${LP_COLORMAP_9:-$DANGER_RED}
 
+    # Debugging flags
+    LP_DEBUG_TIME=${LP_DEBUG_TIME:-0}
 
     # Default config file may be the XDG standard ~/.config/liquidpromptrc,
     # but heirloom dotfile has priority.
@@ -1570,10 +1572,19 @@ prompt_on()
     fi
     if $_LP_SHELL_bash; then
         PROMPT_COMMAND=_lp_set_prompt
+        [[ "$LP_DEBUG_TIME" == 1 ]] && PROMPT_COMMAND="time $PROMPT_COMMAND"
     else # zsh
-        function precmd {
-            _lp_set_prompt
-        }
+        # That doesn't seem to work: no time output
+        #if [[ "$LP_DEBUG_TIME" == 1 ]]; then
+        #    function precmd {
+        #        local TIMEFMT='LiquidPrompt build time: %*E'
+        #        time _lp_set_prompt
+        #    }
+        #else
+            function precmd {
+                _lp_set_prompt
+            }
+        #fi
     fi
 
     # Keep in mind that LP has been sourced