The emission of an event was being logged twice, and the second time was
logging the pickled content of the event. This pickled content contained line
breaks and other things that caused strange output on the client log.

This commit removes the second loggin of the event pickled content.

Closes #7130.

previous regex wasn't capturing addresses of type ipc://<path>

Closes: #7089

We ran into a RuntimeError yesterday on this line, the callback can
modify this dict and make the iteration raise an error. Using keys
method to iterate is safer.
See
http://stackoverflow.com/questions/11941817/python-runtimeerror-dictionary-changed-size-during-iteration-how-to-avoid-th/11941855#11941855

Before this commit, protobuf and protobuf.socketrpc were used to serialize and
transmit messages between events clients. This change implements a simpler ZMQ
client/server events mechanism that uses ZMQ sockets for transmitting messages
from clients to server and to redistribute such messages to subscribed
clients.

Closes: #6359