tests: print expected duration in hwtimer_wait
Ensure hwtimer_spin() won't wait for an unreachable stop counter value
without using a costly MOD operation
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
Use custom assembly code instead of MSP GCC primitives for dINT()/eINT()
and all other functions that enable or disable interrupts
Ensure interrupts are enabled before going in low-power mode
Ensure only GIE bit is touched in splx_()