tests: print expected duration in hwtimer_wait
Merge pull request #1625 from LudwigOrtmann/hwtimer_wait_duration

tests: print expected duration in hwtimer_wait
tests: remove need for pow,log2 in hwtimer_wait

Default to precalculated value for geometric series, so pow and log2
are not needed.
Merge pull request #1617 from rousselk/hwtimer-spin-ovf-fix

Ensure hwtimer_spin() won't wait for an unreachable stop counter value
Merge pull request #1626 from LudwigOrtmann/hwtimer_wait_fixup

tests: remove need for pow,log2 in hwtimer_wait
Make hwtimer_spin() work even with interrupts disabled
by using only 16 significative bits on MSP430 hardware timers