Less flickery colour picker when the dragged value hasn't changed

Only call value_changed_fn when the value has changed during null poll events, in line with the check for change logic in Increment().
Note that steppable_set_value() still sends one event per call as mentioned in the cautionary note at line 535, so when called programmatically the behaviour is unchanged.

Tested on a Raspberry Pi, no more shimmering colour swatches.

Version 0.55. Tagged as 'Picker-0_55'

Support011/c/steppable

@@ -199,8 +199,15 @@ static os_error *Set_Position (steppable_s s, os_coord *pos,
             pos->y + window_state.yscroll - window_state.visible.y1,
             track_state.icon.extent.y0, track_state.icon.extent.y1);
 
-   if ((error = Set_Value (s, value)) != NULL)
-      goto finish;
+   if (value != s->steppable.value)
+   {  if ((error = Set_Value (s, value)) != NULL)
+         goto finish;
+
+      tracef ("steppable calling value_changed_fn\n");
+      if ((error = (*s->steppable.value_changed_fn) (s, value,
+            s->dragging, s->steppable.handle)) != NULL)
+         goto finish;
+   }
 
    if (start_drag)
    {  wimp_drag drag;
@@ -225,11 +232,6 @@ static os_error *Set_Position (steppable_s s, os_coord *pos,
       s->dragging = TRUE;
    }
 
-   tracef ("steppable calling value_changed_fn\n");
-   if ((error = (*s->steppable.value_changed_fn) (s, value, s->dragging,
-         s->steppable.handle)) != NULL)
-      goto finish;
-
 finish:
    return error;
 }

VersionNum

-/* (0.54)
+/* (0.55)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  * Last processed by srccommit version: 1.1.
  *
  */
-#define Module_MajorVersion_CMHG        0.54
+#define Module_MajorVersion_CMHG        0.55
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                07 Aug 2013
+#define Module_Date_CMHG                12 Jan 2014
 
-#define Module_MajorVersion             "0.54"
-#define Module_Version                  54
+#define Module_MajorVersion             "0.55"
+#define Module_Version                  55
 #define Module_MinorVersion             ""
-#define Module_Date                     "07 Aug 2013"
+#define Module_Date                     "12 Jan 2014"
 
-#define Module_ApplicationDate          "07-Aug-13"
+#define Module_ApplicationDate          "12-Jan-14"
 
 #define Module_ComponentName            "Picker"
 #define Module_ComponentPath            "castle/RiscOS/Sources/Video/UserI/Picker"
 
-#define Module_FullVersion              "0.54"
-#define Module_HelpVersion              "0.54 (07 Aug 2013)"
-#define Module_LibraryVersionInfo       "0:54"
+#define Module_FullVersion              "0.55"
+#define Module_HelpVersion              "0.55 (12 Jan 2014)"
+#define Module_LibraryVersionInfo       "0:55"