for generated brushes.
The maximum radius we allowed for generated brushes was not used
consistently everywhere.
In the API call we clamped it to 0.0-32767.0, while the param_spec
set min and max to 0.1 and 4000.0, and the brush editor used a
maximum of 1000.0.
Using a large value (probably anything larger than 4000) would
sooner or later lead to a crash.
Instead of manual changes everywhere, let's define a maximum and
minimum in one place and use that wherever we need the min/max values.
Use the values as set in the param_spec for the defines.
The only place we can't easily do that is in brush.pdb, so we add
a comment above our defines that the values need updating there too.
Actually we should probably use more defines for other values too,
that way there is less chance of min/max values getting out of synch
throughout our code.