Port of libmosquitto for genode

[irgendwie]

Make sure a vde switch is running before executing the example, otherwise it won't work!

• You can test compiling and linking the lib by executing make test/libports/libmosquitto in the build directory
• repos/mpct is a small example, using libmosquitto.
  It connects to a mosquitto server running on 192.168.100.254:1883 and publishes "Hello World" with an increasing iterator, which can be read by connecting another client (sample client provided by mosquitto) and subscribing on "mpct".
• You can run the small example with make run/mpct or just compile it by using make mpct (don't forget to adapt the INC_DIR path in the target.mk file)

Open points:

• the sample example blocks after publishing a few messages (approx. 300 for me)
• random lwip error:
  ... [init -> mpct] Assertion "tcp_write: pbufs on queue => at least one queue non-empty" failed at /home/alex/Projects/genode/contrib/lwip-136ee70f33ffced072262d589c24ab3252d15eff/src/lib/lwip/src/core/tcp_out.c:340 [init -> mpct] void lwip_sleep_forever(): thread 2 ...
• [init -> mpct] int socketpair(int, int, int, int*): socketpair not implemented
  Maybe we can use the workaround used for windows builds
• [init -> mpct] int _sigaction(int, const sigaction*, sigaction*): _sigaction not implemented
  The only signal used is SIGPIPE, which is ignored for windows builds
• [init -> mpct] read_rtc: rtc not configured, returning 0
  rtc is not available on pbxa9 builds 🆘

[irgendwie]

Everything fixed so far and it is runable both with pbxa9 in qemu and on real pandaboard. The freezes are fixed by removing the tcpip_init function (06d4dc1)

• The sigaction error can be fixed by simply removing it -> seems to not be needed by mosquitto (left it in place since the lib is functional with the "broken" signal call)
• rtc, still no idea what to do 🙈

[irgendwie]

Bump version due to https://mosquitto.org/2017/05/security-advisory-cve-2017-7650/