patch for goffice-0.8.7

[jcupitt gmail com]

Hi,

I had to make a couple of changes to go-math.c in goffice-0.8.7 to get
it to build on Windows (actually, mingw cross-compiling from Linux).

It defines go_finitel() as a portability wrapper in case the platform
does not have finitel(), but in a couple of places calls finitel()
directly. I changed these calls to go_finitel() and it built.

http://www.vips.ecs.soton.ac.uk/supported/7.22/win32/goffice-finitel.patch

The man page describes finitel() as obsolete, so perhaps a better fix
would be to switch to the C99 isfinite() instead.

John