Change from `void reboot(void)` to `int reboot(int mode)`.
Move reboot definition to core, rename architecture implementations
from reboot to reboot_arch.
Declare reboot mode(s) in kernel.h, reboot_arch in kernel_internal.h
Currently only one reboot mode is handled, its use is enforced.
Rationale:
A reboot function is already defined in <unistd.h> on BSD systems.
(See: http://www.openbsd.org/cgi-bin/man.cgi?query=reboot&sektion=2)
This patch not only allows native to build sensibly on these systems
but also streamlines RIOTs compatability with existing software.
* introduced dummy function for msp-430 config-save
* moved sysconfig from board to core
[sys/transceiver cpu/]
* moved some buffer size defines to cpu dependent parts
* some cleanups
* increased main priority to the half of maximum priority
* introduced define for minimum stack size
* decreased stack size for uart0 thread
* merged commands for rtc shell module to one command (date)
* cleanup of header includes
