[XForms] Bug in fdesign with spinner bounds

[SBP]

Hi again!

I think I found another bug in fdesign.

When setting spinner bounds via fdesign, they are saved in the .fd
file, but when opening that file the bounds are not loaded. Digging
into the code, I found there's no function in fd_file.c that reads the
bounds. I suspect there's also no function to read the precision nor
other spinner properties. Maybe we should add them?

Cheers!

Sirius.