Orange: more float buffer support;

- Image textures use float colors now, when present. Works for mipmap too,
  and for AO skycolor (probes)
- Backbuffer option uses float buffers too. Note that rendering OSA will
  resample the backbuffer, filtering it... will need to be solved with the
  new composit stage
- LMB sampling in image window now shows float color too

+ bugfix in imbuf, filtering for float buffers had an error.

source/blender/render/extern/include/render_types.h

@@ -49,6 +49,7 @@
 /* ------------------------------------------------------------------------- */
 
 /* localized texture result data */
+/* note; tr tg tb ta has to remain in this order */
 typedef struct TexResult {
 	float tin, tr, tg, tb, ta;
 	int talpha;