1.0.5.39: sb-sprof call counting
* Add support for deterministically tracking the amount of times
that certain functions were called during a sb-sprof profiling
run.
* The goal is to allow people to easily see whether a lot of time
is spent in function X due to it being called often, or due to
the average call being slow.
* The benefit over using sb-profile is that a) the reporting
of the call counts is integrated into the normal sb-sprof
interface and b) there's a lot less overhead, since we're just
counting calls, not tracking cpu usage / consing.