plruby: rb_iterate symbol clash with libruby.so

Hi, I'm curious how it worked before (seems like the function is defined
in both PostgreSQL and Ruby projects for quite some time) - but I recently
came across this situation:

- /bin/postgres is build-time linked with 'ld -E'
- /bin/postgres dlopen()s plruby.so
- plruby.so calls rb_iterate, but linker prefers rb_iterate defined in
/bin/postgres, instead of (the wanted one) rb_iterate from libruby.so

This means an ugly PG server crash. I'm curious what to do with this;
ideally it would be solvable from plruby.so itself, but there doesn't seem
to be nice solution (one could do some hacks with dlopen('libruby.so')).

Is it realistic we could rename red-black tree methods from 'rb_*' to e.g.
'rbt_*' to avoid this clash?

Pavel