Fix: The radial control would fail, in sculpt mode, to set size if object-space sizing was enabled.

This was caused because a small part of sculpt's radial control code did not make it into the new version.  The old code would set a new object-space size by scaling it proportional to how much the new screen-space size was changed.  

The solution I implement here is to do the same scaling inside the RNA callbacks.  This way, users of those properties do not have to worry about inconsistency.

I added a comment warning that brush_set_size, brush_set_unified_size, brush_unprojected_radius, and brush_set_unprojected_radius do not guarantee consistency because it is not always possible to precisely know what the new unprojected radius is in all contexts where you might set the size.  

I would implement the consistency check at the lower level (in those listed functions) but at this time I think it needs to be looked at to make sure that won't cause problems.  In addition, I am not sure that scaling by the ratio of change is strictly correct in all cases.

In any case, this at least fixes the immediate problem.

source/blender/blenkernel/intern/brush.c

@@ -1251,6 +1251,19 @@ static short unified_settings(Brush *brush)
 	return 0;
 }
 
+// XXX: be careful about setting size and unprojected radius
+// because they depend on one another
+// these functions do not set the other corresponding value
+// this can lead to odd behavior if size and unprojected
+// radius become inconsistent.
+// the biggest problem is that it isn't possible to change
+// unprojected radius because a view context is not
+// available.  my ussual solution to this is to use the
+// ratio of change of the size to change the unprojected
+// radius.  Not completely convinced that is correct.
+// In anycase, a better solution is needed to prevent
+// inconsistency.
+
 static void set_unified_size(Brush *brush, int value)
 {
 	Scene *sce;

source/blender/makesrna/intern/rna_brush.c

@@ -28,6 +28,7 @@
 
 
 #include <stdlib.h>
+#include <assert.h>
 
 #include "RNA_define.h"
 
@@ -166,6 +167,13 @@ static void rna_Brush_icon_update(Main *bmain, Scene *scene, PointerRNA *ptr)
 static void rna_Brush_set_size(PointerRNA *ptr, int value)
 {
 	Brush* me = (Brush*)(ptr->data);
+
+	// set unprojected radius, so they remain consistent
+	double size= (double)brush_size(me);
+	assert(size != 0); // paranoia: sanity checks during load and rna make sure we don't divide by zero here
+	float unprojected_radius= (float)(brush_unprojected_radius(me) * (double)value / size);
+	brush_set_unprojected_radius(me, unprojected_radius);
+
 	brush_set_size(me, value);
 }
 
@@ -214,6 +222,13 @@ static int rna_Brush_get_use_alpha_pressure(PointerRNA *ptr)
 static void rna_Brush_set_unprojected_radius(PointerRNA *ptr, float value)
 {
 	Brush* me = (Brush*)(ptr->data);
+
+	// set size, so they remain consistent
+	double unprojected_radius= (double)brush_unprojected_radius(me);
+	assert(unprojected_radius != 0); // paranoia: sanity checks during load and rna make sure we don't divide by zero here
+	int size= (int)((double)brush_size(me) * (double)value / unprojected_radius);
+	brush_set_size(me, size);
+
 	brush_set_unprojected_radius(me, value);
 }