uldn't be reentrant, not without some help from the
     system.
<li> tune/time.c could try to determine at runtime whether
     <code>getrusage</code> and <code>gettimeofday</code> are reliable.
     Currently we pretend in configure that the dodgy m68k netbsd 1.4.1
     <code>getrusage</code> doesn't exist.  If a test might take a long time
     to run then perhaps cache the result in a file somewhere.
<li> tune/time.c could choose the default precision based on the
     <code>speed_unittime</code> determ