Merge pull request #588 from hurtonm/master

Small code cleanup
Added security curve test

Test is skipped if no libsodium.
Added warning if libsodium not configured
Merge branch 'master' of git://github.com/zeromq/libzmq
Merge pull request #589 from ianbarber/master

Add test for CURVE mechanism
Merge pull request #590 from hurtonm/master

Refactor how properties are parsed
Rename parse_properties to parse_metadata