Address “autom4te preselections” testsuite failure

Address “autom4te preselections” testsuite failure

This test failure has the same root cause as described in
commit 3fbfb13e7a846e98fa931b2bce373b5b2364a11b: autom4te
regenerates the output unexpectedly because the output has
the *same* file modification timestamp as the cache file it
was generated from.  Apply the same stopgap fix.

* tests/tools.at (autom4te preselections): Immediately after
  running autoconf the first time, delay and then touch configure.
  Move the “echo newer > newer” line after the comment that explains
  what it’s for.  Insert additional blank lines for readability.