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.
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]
make / cortex m: replace hyphen in module name

When you compile for UDOO, you are greeted by a multitude of this
warnings:
```
<command-line>:0:14: warning: ISO C99 requires whitespace after the macro name [enabled by default]
```

The reason for that is the argument `-DMODULE_CORTEX-M3_COMMON`.

This PR fixes this problem by replacing hyphens with underscores for the
`-D…` argument.
bugfix: msp430 can write now more then one byte to flash
Merge pull request #1348 from SGSSGene/bugfix_writetorom

msp430: fix writing more than one byte to flash
pyterm: made python compatible with python2 and python3

In python 3 there is no implicit converion of bytes to str or character.
Merge pull request #1349 from cgundogan/fix_pyterm_python_version

pyterm: made python compatible with python2 and python3
native: implement hwtimer removal
boards: harmonise cc2420 isr

TelosB, wsn430-v14, Z1
Merge pull request #1304 from thomaseichinger/fix_cc2420_rxfifo_of

boards: harmonise cc2420 isr
Merge pull request #1346 from Kijewski/hyphen-in-modulename

make: cortex m3: replace hyphen in module name
Merge pull request #1301 from cgundogan/fix_tcp_handshake_seq_ack_rfc_compliancy

destiny: wireshark revealed wrong seq/ack nr. in tcp handshake
nativenet: change max packet size to 127

Real IEEE 802.15.4 transceivers have a payload of 127. Hence, for
testing - particular 6lowpan - it would make sense to have the same
limitation in nativenet. Especially to test fragmentation this is
helpful.
cpu cortex-m3_common: cleanup thread_arch.c
cpu - sam3x8e: added switch for newlib-nano specs
Merge pull request #1354 from OlegHahm/nativenet_packetsize

nativenet: change max packet size to 127
Merge pull request #1335 from Kijewski/fix-all-warnings-for-native-and-qemu-i386

Fix all warnings for native and qemu-i386