* lib/m4sugar/m4sh.m4 (_AS_PATH_SEPARATOR_PREPARE): Set FPATH too.
Problem reported by Fred Kreek in
<http://lists.gnu.org/archive/html/bug-autoconf/2007-06/msg00009.html>.
* doc/autoconf.texi (Special Shell Variables): Warn about FPATH.
(Macro Names, Defining Directories): Don't mention PATH as a name
for a fully qualified file name, as this usage violates the GNU
coding standards and we shouldn't recommend it.
* lib/autotest/general.m4 (AT_INIT): Don't set PATH to the empty
string and then assume shell builtins like "test" will work.