Rotation constraint update.

Small fix, but results are at least less frustrating now. It uses the
"compatible euler" function from inserting key positions here, preventing
euler values to be constrainted that differ weirdly.

I've tried several other approaches to get a definite rotate constraint,
but only constraining a single axes seems to me impossible magic still...

source/blender/include/BDR_editobject.h

@@ -74,7 +74,6 @@ void apply_object(void);
 
 /* old transform */
 void apply_keyb_grid(float *val, float fac1, float fac2, float fac3, int invert);
-void compatible_eul(float *eul, float *oldrot);
 void headerprint(char *str);
 /* used for old game engine collision optimize */
 int cylinder_intersect_test(void);