guile-gtk bugs

[Kevin Ryde]

I applied a couple of bug fixes.  The latter is particularly nasty, I
was ending up with one symbol at 0xB700000 and another at 0x0800000,
causing the wraparound.  No doubt it depended on load order, and what
memory malloc delivered back, etc, etc.

        * gtk-1.2.defs (GtkWidget): Correction to requisition-width,
        requisition-height; were opposite way around.

        * guile-gtk.c (sgtk_flags_comp): Correction to comparison, subtraction
        to a signed result is wrong when values are more than 2^31 apart,
        because the value wraps around to the opposite sign.  This was seen on
        i386 in certain circumstances, causing flags to be unrecognised by
        sgtk_enum_flags_bin_search.