core: sched: thread: optimize thread status field usage

see PR #716 for discussion
sys: update ps to reflect thread status variable changes
core:mutex: remove refactor remnant
Merge pull request #858 from Kijewski/mutex-clutter

core:mutex: remove refactor remnant
Merge pull request #725 from kaspar030/optimize_thread_status_usage

core: sched: thread: optimize thread status field usage
include needed stdint.h
Merge pull request #865 from thomaseichinger/redbee-econotag_fix_board_h

redbee-econotag: include needed stdint.h