Drop gratuitous differences from 3.1.0 .

Earlier I said this was based on 3.1.3, but actually it's 3.1.0 .

* config.h
  Add this, as libspamc.c expects to include it.  Define autoconf macros it
  expects.  Move includes and declarations for my code here.

* libspamc.c
  Drop gratuitous differences.

* libspamc.h
  Only declare libspamc_log if libspamc_log isn't defined as macro (in
  config.h), same as libspamc.c .