Add a new loader(8) variable, twiddle_divisor, allowing control over the
output frequency of the "twiddle" IO progress indicator.  The default
value is 1.  For larger values N, the next stage of the animation is only
output on every Nth call to the output routine.  A sufficiently large N
effectively disables the animation completely.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@276087 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f