tests: fix spurious failure due to missing sleeps

tests: fix spurious failure due to missing sleeps

Fixes automake bug#14528.

* THANKS: Give credit to that bug's original reporter.

* t/remake-configure-dependencies.sh: Add few missing '$sleep'
invocations.  I thought that the sleeps implicit in the configure
invocation were enough, but they were not, actually.  Here is what
can happen:

  1. The config.status script is generated by a configure run.
  2. ./config.status and make are run.
  3. The 'print-version' script is modified.
  4. Since that script is listed in $(CONFIGURE_DEPENDENCIES),
     autoconf is re-run.
  5. On a fast-enough machine, the three steps 2-4 above, even
     combined, might have taken less than a second to run;
  6. If the filesystem doesn't have a sub-second timestamp
     resolution, that means the newly-generated configure has
     the same timestamp of the old config.status;
  7. So, config.status is not re-run, and the Makefiles are
     not updated.
  8. Spurious failure!

So we really need more explicit sleeps.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>