Changes to "evaluation time" for Curves:

After discussions with Campbell regarding #24336 and #24309, we've decided to make this property for curves to only get set when an F-Curve explicitly animates it. 

As a consequence...
- ALL OLD FILES using follow-path constraints that depended on this changed behaviour will currently need manual patching to add an appropriate F-Curve
- Ctrl-P (Parenting to Curves -> Follow Path option) will now automatically create such F-Curves mimicking the old behaviour so that creating camera-following-path setups still works smoothly.
- Directly adding a Follow Path constraint bypasses this, so you'll need to manually add such F-Curves if you need them.

The main problem with the old approach was that there were many cases in which curve data could get added but the ctime would be incorrect until a frame change (i.e. on render) flushed this.

source/blender/editors/curve/editcurve.c

@@ -6018,7 +6018,6 @@ static int curvesurf_prim_add(bContext *C, wmOperator *op, int type, int isSurf)
 
 			cu= (Curve*)obedit->data;
 			cu->flag |= CU_DEFORM_FILL;
-			cu->ctime= CFRA;
 			if(type & CU_PRIM_PATH)
 				cu->flag |= CU_PATH|CU_3D;
 		} else DAG_id_flush_update(&obedit->id, OB_RECALC_DATA);