Use default compiler for nightly testing

Server that runs nightly tests was updated and the compiler used for
nightly testing stopped working due to missing libraries. Let's use the
distribution shipped compiler, which is new enough for NUL (GCC 4.7.2).
Fix nightly documentation build

It's no longer necessary to use custom-built doxygen.
Update expired SSL certificates (for libvirt testing)
Fixed warning.
Fixed potential RX queue mishandling.

When more than half of the RX queue was used, the old code stopped processing packets
to avoid monopolizing CPU time. In this situation we re-raise the IRQ again to come
back later.
Increase queue lengths to realistic sizes.
Jacek says this devices works fine. :)
Warn only once on receiver overrun. Since the queue is now pretty long, this should be very rare.
GCC 4.9 introduced __cxa_throw_bad_array_new_length. Fixes #19. (If not please reopen.)
Updated git submodule repositories to publicly available URLs.