Matcap support in 3D Viewport.

Full log is here:
http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.66/Usability#Matcap_in_3D_viewport

Implementation notes:

- Matcaps are an extension of Solid draw mode, and don't show in other drawmodes.
  (It's mostly intended to aid modeling/sculpt)

- By design, Matcaps are a UI feature, and only stored locally for the UI itself, and
  won't affect rendering or materials.

- Currently a set of 16 (GPL licensed) Matcaps have been compiled into Blender. 
  It doesn't take memory or cpu time, until you use it.

- Brush Icons and Matcaps use same code now, and only get generated/allocated on
  actually using it (instead of on startup).

- The current set might get new or different images still, based on user feedback.

- Matcap images are 512x512 pixels, so each image takes 1 Mb memory. Unused matcaps get 
  freed immediately. The Matcap icon previews (128x128 pixels) stay in memory.

- Loading own matcap image files will be added later. That needs design and code work 
  to get it stable and memory-friendly.

- The GLSL code uses the ID PreviewImage for matcaps. I tested it using the existing
  Material previews, which has its limits... especially for textured previews the
  normal-mapped matcap won't look good.

source/blender/editors/include/UI_interface.h

@@ -807,6 +807,7 @@ uiLayout *uiTemplateModifier(uiLayout *layout, struct bContext *C, struct Pointe
 uiLayout *uiTemplateConstraint(uiLayout *layout, struct PointerRNA *ptr);
 void uiTemplatePreview(uiLayout *layout, struct ID *id, int show_buttons, struct ID *parent, struct MTex *slot);
 void uiTemplateColorRamp(uiLayout *layout, struct PointerRNA *ptr, const char *propname, int expand);
+void uiTemplateIconView(uiLayout *layout, struct PointerRNA *ptr, const char *propname);
 void uiTemplateHistogram(uiLayout *layout, struct PointerRNA *ptr, const char *propname);
 void uiTemplateWaveform(uiLayout *layout, struct PointerRNA *ptr, const char *propname);
 void uiTemplateVectorscope(uiLayout *layout, struct PointerRNA *ptr, const char *propname);