Trouble compiling Bro release 0.8a48 on OpenBSD3.3

I get a segmentation fault now :(... Do I need to load some
additional files to process the signature rules converted from

Yes, per the comment in policy/sigs/ex.web-rules.sig, you need to also
load snort.bro and signatures.bro (as well as mt.bro).

When I do this, it works for me; but I don't get a core dump if I leave
them off, either.

In general, when reporting Bro bugs it really helps if you can include a
tcpdump trace (perhaps generated using bro -w) that reproduces the problem.