Corrected return values of zeroconf client in order to return true-evaluable values. related to #4051

we have that in all files. To at least lesser the confusion a bit, add
vim tags for that.
Additionally, fix wrong #! in a few files.

socket module doesn't have AI_ADDRCONFIG attribute under windows

use timeout_add_seconds instead of timeout_add (when it's available), more efficient. fixes #3734, #3736

Reverting [9324]. Reopen #3734.

Backport some fixes to zeroconf: don't fail on special characters, don't allow gpg usage when it is not secure or even possible
Be more verbose when there is a key missmatch.

Mind that presence in zeroconf are not signed, gpg keys have to be assigned manually therefore.

Refactor the way we decide whether GPG is usable or not: Ability to change keys when no valid passphrase could be entered.
See #1210. Workaround for unavailable keys.

Remove useless except block: import of GnuPGInterface is the same on Debian and non Debian systems.

remove useless config option usegpg

Fix #3241.