Fixes bug 17924; bugfix on 0.2.4.1-alpha.
In ddf5020ea8, we added config.log to CLEANFILES in doc/Makefile.am
so that distcheck would be happy about the presence of doc/config.log.
But when we moved to nonrecursie makefiles in 2a4a149624, we
accidentally left that filename unchanged, so that it referred to
config.log instead.
Patch from cypherpunks.
