[gnome-calculator] Reset text in new function name input box.

[Arth Patel <arthpatel src gnome org>]

commit 22dbc47516e6d8048594cdf38e75c7e594d51b87
Author: PioneerAxon <arth svnit gmail com>
Date:   Thu May 29 02:45:42 2014 +0530

    Reset text in new function name input box.
    
    Original patch submitted by ZZromanZZ gmail com 
    See Bug #729699 for more details.

 src/math-function-popup.vala |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)
---
diff --git a/src/math-function-popup.vala b/src/math-function-popup.vala
index b7c4149..0974941 100644
--- a/src/math-function-popup.vala
+++ b/src/math-function-popup.vala
@@ -14,7 +14,10 @@ public class MathFunctionPopup : Gtk.Window
 
     private Gtk.ScrolledWindow scrolled_window;
     private Gtk.Box vbox;
+
     private Gtk.Entry function_name_entry;
+    private bool function_name_entry_placeholder_reseted = false;
+
     private Gtk.Button add_function_button;
     private Gtk.SpinButton add_arguments_button;
 
@@ -62,6 +65,7 @@ public class MathFunctionPopup : Gtk.Window
         function_name_entry = new Gtk.Entry ();
         function_name_entry.set_text ("Type function name here");
         function_name_entry.key_press_event.connect (function_name_key_press_cb);
+        function_name_entry.button_press_event.connect (function_name_mouse_click_cb);
         function_name_entry.changed.connect (function_name_changed_cb);
         function_name_entry.set_margin_right (5);
         function_name_entry.activate.connect (add_function_cb);
@@ -99,8 +103,21 @@ public class MathFunctionPopup : Gtk.Window
         widget.get_toplevel ().destroy ();
     }
 
+    private bool function_name_mouse_click_cb (Gtk.Widget widget, Gdk.EventButton event)
+    {
+        if(!this.function_name_entry_placeholder_reseted)
+        {
+            this.function_name_entry_placeholder_reseted = true;
+            this.function_name_entry.set_text ("");
+        }
+
+        return false;
+    }
+
     private bool function_name_key_press_cb (Gtk.Widget widget, Gdk.EventKey event)
     {
+        this.function_name_entry_placeholder_reseted = true;
+
         /* Can't have whitespace in names, so replace with underscores */
         if (event.keyval == Gdk.Key.space || event.keyval == Gdk.Key.KP_Space)
             event.keyval = Gdk.Key.underscore;