Set ready exiting from the scope early

so that the main thread won't deadlock on self.ready if bad things happen.
Merge pull request #614 from rainwoodman/patch-3

Set ready exiting from the scope early
Quick fix in case of new host
Use SSHException
Merge pull request #615 from SylvainCorlay/new_ssh_key

Handling the case of a new ssh host

closes #589
cloning a repo takes more time than downloading bare copy of source code.
usage of mirrors has been deprecated since pypi is behind a CDN
Merge pull request #616 from ticosax/speedup-ci

Speedup ci
libzmq-4.1 changed default LINGER
Merge pull request #617 from minrk/linger-changed

libzmq-4.1 changed default LINGER
use travis-built wheels

for quicker installation
Fix GC after-fork bug
Merge pull request #618 from minrk/fork-gc

Fix GC after-fork bug