vtimer: fix callback usage

There is no need to test the "handler" set in the vtimer struct, and
have some code executed then. We just can make the code to execute the
handler. To lengthy `if else if`, just a call.
lpc1768: cleanup Makefile

`cpu/lpc1768/Makefile` contains many lines that don't belong into this
file, but the maybe `Makefile.include`. Either way, this Makefile is
never called with these goals.
make: refactor make system (parallelism, deduplication)

Almost everything was build sequentially in RIOT, because we employed
explicit for-loops to build directories (DIRS). This PR makes our make
system use normal dependencies to build directories.

All our compiling rules were duplicated, once for the application, once
for modules. This PR makes the application a normal module, removing
this duplication.
make: make DIRS usable for applications
make: create dependencies as side effect
make: use abspath for better error messages
destiny: wireshark revealed wrong seq/ack nr. in tcp handshake
Capturing the tcp handshake with wireshark revealed that the
sequence and ack nrs. are not rfc compliant.
I did the changes based on
http://tools.ietf.org/html/rfc793#page-52 to http://tools.ietf.org/html/rfc793#page-72
Merge pull request #1326 from Kijewski/make-parallel-dirs

 make: refactor make system (parallelism, deduplication)
x86: shutdown on LPM_POWERDOWN
Fix all warnings for native and qemu-i386

Missing returns, unused variables (only used for debugging), empty
translation units, missing function prototypes, and GNU extensions.
drivers: added set_absolute to timer interface
Merge pull request #1289 from haukepetersen/fix_drivers_periph_timer

drivers: added set_absolute to timer interface
make: OSX: don't fail for empty .a archives

Fixes issue #1333.
tests/Travis: run unittests on x86, too
Merge pull request #1252 from Kijewski/travis-x86

tests/Travis: run unittests on qemu-i386, too
Merge pull request #1334 from Kijewski/issue-1333

make: OSX: don't fail for empty .a archives
Changed RIOT/Makefile.include, Makefile.base, Makefile.cflags, and native/Makefile.include to compile C and C++ files.
added riot_and_cpp example
added sudo apt-get install g++-multilib to travis.yml
Merge pull request #981 from vanhieubk/nhat_mixCompiler

Another way to mix c and cpp in user app with RIOT [native]