Small addition to stretch minimize: with pad +/- or the wheel mouse

you can now blend between the original and minimized.

Stretch minimizing trades conformality (= perfect squares in checkerboard
texture) for a better sampling of the texture (= often not so well shaped
checkerboard), so it is useful to let the user find a balance between the
two.

source/blender/src/parametrizer.h

@@ -59,6 +59,7 @@ void param_lscm_end(ParamHandle *handle);
 /* Stretch */
 
 void param_stretch_begin(ParamHandle *handle);
+void param_stretch_blend(ParamHandle *handle, float blend);
 void param_stretch_iter(ParamHandle *handle);
 void param_stretch_end(ParamHandle *handle, ParamBool restore);