theme loading on HPUX has "issues"

[Dan Newcombe <Newcombe mordor clayton edu>]

In gtk/gtkthemes.c, there is

	g_snprintf (fullname, 1024, "lib%s.so", name);

This is assuming that shared libraries always end in .so   On HPUX, they
end in .sl  Of course, pretty much everywhere else, they are .so, but HSUX
:)