Do not zero out sched_threads needlessly

The function sched_init() zeroes out sched_threads needlessly. All
static variables can be assumed to be initialized with zero, anyways.
The C standard mandates it, and all at other places in the code it is
assumed.
Add a reboot() function to kernel.h definitions.
Implemented reboot() function for MSP430 MCUs
Add wireshark dissector for native packets
core: msg: don't wake up sender after receive if it's REPLY_BLOCKED

solves issue #100

If the sender is reply-blocked, waking it up after its message has been
delivered is wrong. It needs to stay reply-blocked until the reply has
been delivered.
core: msg: add some debug statements
actually use msg_queue in ip.c

msg_queue is defined but never used, hook it up so IP packets get queued instead of dropped when there is more than one.
change the name to ip_msg_queue to avoid naming conflicts.
also add msg_queue for UDP

All other layers in the network stack use a msg_queue to not drop messages, which in this context represent packages.
This finally fixes the random crashes when UDP network traffic is present. Turns out RIOT is not handling lost messages well.
core: msg: yield after queueing of a message if REPLY_BLOCKED

When setting the running task reply_blocked, it is implicitly removed
from the runqueue. But if queueing of a msg is actually successful, the
thread exits msg_send without yielding, continuing to run even if it's
not supposed to.

Nice example of why multiple function exit points lead to weird
errors...
Use `filter` instead of `findstring`

See #672
Function attributes are now defined elsewhere ("attributes.h")
Implemented reboot() function for ARM-based MCUs
Added while(1) to ensure GCC valids NORETURN; fixed indentation
Eliminate findstring in more places
https://github.com/Kijewski/RIOT/commit/102dc453828012985f82915ad826be069f444e61#commitcomment-5378590
implement rudimentary native reboot
Added while(1) to ensure GCC valids NORETURN; fixed indentation
Merge pull request #1 from LudwigOrtmann/native_reboot

implement rudimentary native reboot
add system calls to the shell
Merge pull request #2 from LudwigOrtmann/shell_syscalls

add system calls to the shell (to implement a reboot command)