* alocal.in: Use Automake::Configure_ac.

* alocal.in: Use Automake::Configure_ac.
($configure_ac): Delete.
(scan_configure): Adjust use of find_configure_ac;
* automake.in: Use Automake::Configure_ac.
($configure_ac): Delete.
(scan_autoconf_files): Adjust use of find_configure_ac;
* lib/Automake/Configure_ac.pm: New file.
* lib/Automake/General.pm (find_configure_ac): Delete.  Now
replaced by Automake::Configure_ac::search_configure_ac.
* lib/Automake/Makefile.am (dist_perllib_DATA): Add Configure_ac.pm.
* lib/Automake/Variable.pm: Use Automake::Configure_ac.
(require_variables): Adjust use of $configure_ac.