Workaround for possible bug in ctxsw()

Something is wrong w/ prnull's initial stack layout or SP value.
If the first call to resched() occurs from prnull, prnull's SP becomes
corrupt and the next time it is selected for execution the PC will be
somewhere random in memory.

Experimentally, I found that forcing the first call to resched() to
occur from an IRQ handler (timer in the case of the raspberry-pi)
avoids this issue.
Revert "Fix for ctxsw"

This reverts commit f80caabaf9de64e84ef62f702f9ef00336739412, to be replaced by cleaned up version: 8e12392c04c867e06e36003bf3977b8c05dd0e94
Merge branch 'ctxsw_bug' into team_redundancy_team