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
shell: added command to print all ignored addresses
Merge pull request #1337 from OlegHahm/print_ignore

shell: added command to print all ignored addresses
destiny: set ack bit for (almost) all segments after syn
The current implementation does not set the ack bit
for outgoing data segments and the fin segment.

However, RFC793 states that all segments
should have an ack bit set in order to present a valid
ack nr. in outgoing segments.

Currently, data segments and acknowledgement segments
are distinguished by the existence of their ack bit.
With the new assumption, that both of these types of
segments need an ack bit set, I had to change several
parts of the current implementation to make this
decision by inspecting the payload size.

destiny: added parens
Merge pull request #1321 from cgundogan/fix_missing_ack_bit

destiny: set ack bit for (almost) all segments after syn
Merge pull request #1326 from Kijewski/make-parallel-dirs

 make: refactor make system (parallelism, deduplication)
x86: shutdown on LPM_POWERDOWN
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]