* Makefile.maint (sc_root_tests): Use recommend style s/a/b/ for
sed substitutions.
* doc/autoconf.texi (Installation Directory Variables): Use s|a|b|
for file names, again. Reported by Noah Misch.
(Coding Style): Explain that s|a|b| is preferred for file names.
* lib/autoconf/status.m4 (_AC_OUTPUT_FILES_PREPARE): Prefer s/a/b/.
(AC_OUTPUT_MAKE_DEFS): Likewise.
* lib/autotest/general.m4 (AT_INIT): Likewise.
* lib/m4sugar/m4sh.m4 (_AS_LINENO_PREPARE): Likewise.
* tests/local.at (AT_CHECK_AUTOM4TE): Likewise.