Add buildbot hacks for OpenBSD.
Add buildbot hacks for OpenBSD.

OpenBSD auto{conf,make} want a version specified in the environment
for each of the tools.  For now, hardwire this into autogen.sh until
we can figure out a better way of dealing with this.

dscho/nmh,mcr/nmh,mcr/nmh,dscho/nmh,dscho/nmh,dscho/nmh