Release of BOPM 3.1.3

I just released BOPM 3.1.3. This just a bug fix release and there is
no need to update if your BOPM is running ok, the main changes are:

- Fix misuse of lvalue in libopm that didn't compile on GCC 4.
- Remove references to opm.blitzed.org and suggest people try
  various alternative DNSBLs, including DroneBL.
- Update to newer versions of automake/autoconf/libtool

You can get it from the usual place (http://wiki.blitzed.org/BOPM).
If you have any issues with this release please let me know.

David