native cpu fixes

init hwtimer with interrupts enabled
more error checking for hwtimer
fix signal handler init in hwtimer
error checking for irq (not necessary yet afaik)
native cc110x_ng placebo
removed posix real-time extension timers from cpu
Merge remote-tracking branch 'upstream/master'

Conflicts:
	Makefile.dep
move native board specific parts to corresponding Makefile
fix stack and interrupt bugs
interrupt handling rewrite
(including uart0 integration, rt-extension removal)
Merge remote-tracking branch 'upstream/master'
increase MINIMUM_STACK_SIZE to allow for DEBUG
add missing newline in debug output
generalize .S compilation target flags
inital OSX support for native port
Merge remote-tracking branch 'upstream/master'
use NSIG macro from signal.h for number of signals
Merge remote-tracking branch 'upstream/master'
remove cruft in Makefile.base
Merge pull request #37 from LudwigOrtmann/master

fix context switching, osx support, uart0 support in native port