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/intern/include/pixelshading.h

@@ -73,7 +73,6 @@ void shadeSkyPixel(RE_COLBUFTYPE *collector, float fx, float fy, float *rco);
 void shadeSkyPixelFloat(float *colf, float *rco, float *view, float *dxyview);
 
 void renderSpotHaloPixel(float x, float y, float *target);
-void fillBackgroundImage(RE_COLBUFTYPE *collector, float x, float y);
 void fillBackgroundImageChar(char *col, float x, float y);
 
 /* ------------------------------------------------------------------------- */