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

send stream:features in zeroconf network, and send stanza only when other part reply to stream initialization. fixes #3057

Removing all calls to sys.exc_clear(). This is only necessary in very rare circumstances, and if there is such a circumstance, it should be clearly documented in code.

fix reference in connection_handlers