Problem: zlist_destroy crashing when using push and autofree

zlist_push actually contrary to the documentation doesn't do strdup and
therefore when destroying zlist which had some elements pushed in,
program crashes with double free during purging of items.

Solution: Add strdup where it belongs.
Merge pull request #851 from lovmoen/master

Problem: zarmour's z85 implementation is dependent on libzmq version
Merge pull request #850 from miska/master

Problem: zlist_destroy crashing when using push and autofree