[packages] tinc: contribution from linus.luessing@web.de - configuration via uci...

[packages] tinc: contribution from linus.luessing@web.de - configuration via uci similar to OpenVPN package

With this commit configuration via uci, similiar to the one used for
OpenVPN, will be added to tinc.

Most of the parameters are working just as described in the official
manpages of tincd and tinc.conf as provided by its developer.

The only exceptions are 'disabled' which if set to 1 will make the
init script completely ignore this tinc network and/or tinc host
and 'generate_keys' which if set to 1 will check whether
a key pair is already present for the given tinc network and if not will
generate them with the key size of "key_size" (default if not present:
2048) - this reduces the "effort" of setting up a tinc VPN on a router
to just providing the right uci config file with no need of creating
custom initialization scripts for for instance the key generation.

Furthermore, similiar to the OpenVPN configuration, also tinc configs
of its native format can be used. They just need to be placed in
/etc/tinc/NETNAME. The init scripts will always copy the content of
/etc/tinc/ to /tmp first and will append any parameters provided in
/etc/config/tinc afterwards (the user needs to take care to not specify
non-list parameters in both uci and native config).

(Trivial note: not working URLs of old repositories have been removed from Makefile for downloading sources)

git-svn-id: svn://svn.openwrt.org/openwrt/packages@29137 3c298f89-4303-0410-b956-a3cf2f4a3e73