As PROVIDES can be used to replace real packages now, we don't need the
virtual packages as workaround anymore. This also means that the providing
packages don't need to be added to site.mk explicitly anymore when the
default provider is used.

Allow to use PROVIDES to replace existing packages.

LEDE has sha256sum enabled by default.

This reverts commit dcff6802.

The added debug information is stripped of during packaging, so it does not
increase the package size. It does however slightly change offsets in the
code, preventing the weird ash segfaults we've been seeing. Also, if the
issue returns, we'll have debug information matching the coredumps.

Fixes #1164

Based-on-patch-by: Christof Schulze <christof.schulze@gmx.net>

While we use the hexadecimal representation as a hash input for simplicity,
it should not be interpreted as case-sensitive.

The new proto will simplify the switch to VXLAN encapsulation.

The next-node MAC address doesn't need to be unique in different
communities, so we can as well add a default value.

`make show-release` can be used to discover the current release in scripts.

A bug in batman-adv can lead to a large amount of management traffic being
exchanged between nodes when the multicast optimizations are enabled,
effectively making the mesh unusable. It's safer to disable the feature
for now, until we have a real fix.

sha512sum doesn't add much code that is not also used by sha256sum, but the
change of the configuration hides the segfault issue described in:

  https://bugs.lede-project.org/index.php?do=details&task_id=822

While the issue only seemed to affect dhcpv6.script, it would clutter /tmp
with coredumps, eventually leading to OOM.

This patch got lost in the OpenWrt -> LEDE transition and fixes flash
writes on new UBNT PicoStations.

The SSID for the mesh network should be cryptic, otherwise some users will try to connect to that network and have a bad user experience.

The used nodejs 4.4.5 needs at least GCC 4.8 to be build
https://github.com/nodejs/node/blob/v4.x/BUILDING.md



Signed-off-by: Matthias Fritzsche <matthias@chemnitz.freifunk.net>
[Matthias Schiffer: moved information to the first section]

Allow the autoupdater to work when updating from the removed targets.