Using RTLD_LOCAL instead of RTLD_GLOBAL when dlopening libgtk-x11-2.0
in gtk2_interface.c reduces the startup time of a simple JFrame application
with GTK L&F by about 100ms: approx 1.6s vs 1.7s (on solaris sparc).
There's no apparent reason why we use GLOBAL here anyway.

For the record, here's the startup numbers for native gtk app vs
java app with Ocean and GTK L&F on solaris sparc (Sunblade 2000, Solaris 10):
    native gtk 0.157s
    ocean L&F 0.562s
    gtk L&F 1.707s
    gtk L&F+LOCAL 1.600s

I've attached both java and native gtk apps.