dont rely on boards/Makefile.base
proper inttype runtime, declare to import

define runtime long as hwtimer_now() uses long
import hwtimer.h instead of declaring hwtimer_now()
rename runtime to reflect the unit of measurement
make ps includes adhere to coding convetions
Merge pull request #334 from LudwigOrtmann/scheduler_clean_fix

scheduler: use proper inttype for runtime, use import instead of declaration, rename to runtime_ticks
Merge pull request #340 from LudwigOrtmann/ps_includes

make ps includes adhere to coding convetions
Merge pull request #332 from LudwigOrtmann/buildtest_update

buildtest: dont rely on boards/Makefile.base