* lib/Autom4te/General.pm: (&catfile, &canonfile)

* lib/Autom4te/General.pm: (&catfile, &canonfile)
(&file_name_is_absolute): New, wrappers around routines from
File::Spec.
Use and export them.
(&find_configure_ac): Optionally take a directory where to look at.
* bin/autoreconf.in (&parse_args): Trim the configure.ac part of
the arguments.
Default @ARGV to `.', not find_configure_ac.
(&autoreconf): Argument is a directory.
Trace AC_CONFIG_SUBDIRS and schedule the subdirs for autoreconf'ing.
* doc/autoconf.texi (autoreconf Invocation): Update.