Avoid sleeping for one second most of the time in sanity check.

Avoid sleeping for one second most of the time in sanity check.

* m4/sanity.m4 (AM_SANITY_CHECK): Try sanity check first without
sleeping for a second, and only if that failed, sleep and try
again, to avoid the delay in the common case of a configure
script that is older than a second, or a system with sub-second
time stamp granularity.
Report and different patch by Jim Meyering.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>