batman-adv & alfred 2016.2.

Now really fixes the build on Debian Jessie...

Allow to build Gluon with GCC 4.7 (e.g. on Debian Wheezy) as host compiler
again.

Make pkg-config, mkimage and gcc build with GCC 6 as host compiler. Fix
miscompilation of node.

Fixes #755

Should be redundant after 0bd0df6f

LuCI's authentication won't work without rpcd, but we aren't using the
authentication anyways. Users who need it can just install rpcd explicitly.

Fixes #452

Apart from replacing a patch for the former by two patches for latter,
this involved minimal adaptations of the lua scripts in the following
packages:

* gluon-announce
* gluon-announced
* gluon-mesh-batman-adv-core
* gluon-status-page

This also updates batman-adv & alfred to 2015.1

This should workaround batman-adv's inability to deal with different MTUs
which need fragmentation.

Fixes #435