Copy cf/aclocal.m4 to this file. This should help to sort out autoconf 2.5.x
problems found by Joao for AT branch.
Note, Rafael did this copy before for the AM-LT branch, and the result
propagated to the AT branch, but that was an old version of cf/aclocal.m4
which Maurice has since upgraded to make it compatible with autoconf 2.5.x..