Fixed ae.c to increase performances under FreeBSD ( gettimeofday -> clock_gettime )

On FreeBSD calling gettimeofday() causes all the cores on a multicore
system to be synchronized. On a heavily loaded system with a
significantly CPU bound application this can cause a 40% overall
system degradation.
A better option is to use clock_gettime() and pass in the
CLOCK_REALTIME_FAST clock as the clock to use. This achieves the
same behavior as gettimeofday() on Linux.