Solaris 2.6 finite() prototype

[Andrew Halper <ashalper acm org>]

Probably nobody cares about this except me, but the Linux math.h
finite() function is prototyped in ieeefp.h on Solaris 2.6 SPARC, which
results in a bunch of compiler warnings like:

../lib/geometry.h: In function `check_bb_x':
In file included from ../lib/object.h:30,
                 from ../lib/diagramdata.h:26,
                 from ../lib/filter.h:25,
                 from recent_files.h:25,
                 from recent_files.c:32:
../lib/geometry.h:237: warning: implicit declaration of function
`finite'

Yes, I probably shouldn't be building on Solaris 2.6 SPARC anyway, but
there's a lot of old firesale hardware around here, and it's actually
the most up-to-date UNIX we have here at work.

I'll try to make an unobtrusive patch to fix it.

Andy