zbeacon: uses only interfaces that are running

Adds a check in s_get_interface to ignore the interfaces that do not
have the IFF_UP flag set.
zbeacon: Adds virtual interface "*"

If zsys_interface() is set to “*”, make the beacon broadcast to
INADDR_BROADCAST and bind to INADDR_ANY
zbeacon: Ignore interfaces that are bonding slaves

Ignore interfaces that have the IFF_SLAVE flat set, if this flag is
defined.
Merge remote-tracking branch 'upstream/master'
Merge pull request #570 from pijyoi/master

workaround warning of non-constant static initializer
Test logging was being lost
Regenerated zgossip_server_engine
Updated man pages
Merge pull request #571 from hintjens/master

Small improvements
Clarified zgossip protocol grammar
Minor documentation fixes
Merge pull request #573 from hintjens/master

Minor documentation changes
Merge branch 'master' of https://github.com/ahhentz/czmq
Adds monotonic clock implementation for OSX

Mac OSX does not have clock_gettime(). This adds a monotonic clock
implementation based on this stackoverflow answer

http://stackoverflow.com/questions/11680461
Merge pull request #576 from ahhentz/bugfix

Adds monotonic clock implementation for OSX
zbeacon.c: Remove unused variable in s_get_interface (mingw)

Related issues: #564
Merge pull request #578 from jtanx/win32

zbeacon.c: Remove unused variable in s_get_interface (mingw)
Define class export explicitly
Fixes to travis.yml
Fixed syntax error in .travis.yml