fix signal handler context switch
Merge pull request #245 from LudwigOrtmann/fix_tramp

fix signal handler context switch
use CREATE_WOUT_YIELD on uart0 thread creation

This should remove a race condition in the case that some uart event
occurs after the uart0 thread has started and before control has
returned to the calling thread, as uart0_handler_pid would not have
been set yet.
break long line
Merge pull request #257 from LudwigOrtmann/uart0_thread_create

use CREATE_WOUT_YIELD on uart0 thread creation
implement graceful shutdown in native
Merge pull request #258 from LudwigOrtmann/native_shutdown

implement graceful shutdown in native
improve native README
Merge pull request #261 from LudwigOrtmann/native_README_update

improve native README
merge thread_measure_stack_usage declarations
Merge pull request #260 from LudwigOrtmann/merge_thread_measure_stack_usage_declarations

merge thread_measure_stack_usage declarations
normalize stack defines
add rtc_time function in public header
add rtc_time implementation for native
Merge pull request #267 from LudwigOrtmann/issue_223

normalize stack defines
add time delta to hwtimer
Merge pull request #249 from mehlis/time-rtc

add rtc_time function
Merge pull request #264 from LudwigOrtmann/native_hwtimer_delta

add time delta to hwtimer
posix: add semaphore implementation
remove sixlowpans own semaphore and use new riot semaphore in flowcontrol