All zauth commands are now synchronous

This means caller waits for signal (zsock_wait()) after each command,
which ensures actor finishes its work before the calling thread continues.
Otherwise, the caller will run ahead and attempt to use actor functionality
that isn't ready yet. zproxy works the same way.
Rewrote zproxy class to use zactor model

Existing API is deprecated and moved to zproxy_v2. The new actor based
API is slightly more verbose than the old one. Sorry about this.
Fix segfault in zbeacon (#596)
Merge pull request #598 from ahhentz/zinterface

Fix segfault in zbeacon (#596)
Fix zbeabon s_get_interface() for when zsys_interface() returns "".
Merge pull request #599 from mrvn/pull-zbeacon_get_interface_fix

Fix zbeabon s_get_interface() for when zsys_interface() returns "".
Merge pull request #597 from hintjens/master

zproxy re-implemented as actor
Added temporary tracing for zbroker
Log messages should only show when verbose
Merge pull request #602 from hintjens/master

Some logging fixes / additions
Fix MSVC build breaks.
Change ULL suffix to LLU for portability to MSVC2010/2012.
Make explicit lossy numeric cast.
Add missing comma and try again.
Merge pull request #604 from evoskuil/master

Fixes MSVC build breaks.
Create new class for doubly linked lists.
Merge pull request #600 from Q-Leap-Networks/pull-zdlist

Create new class for doubly linked lists.
New code wasn't working with ZMQ v2
Merge pull request #606 from hintjens/master

New code wasn't working with ZMQ v2
zdlist: Indentation: convert tabs to 8 chars
zdlist: add spaces before (
zdlist: blank line before method declaration