zcurve: fix unused variable errors

Fix serveral places where zcurve build would fail because
of unused variables if libsodium not enabled.
zsockopt: fix prototype mismatch

Build fails if GCC -Werror because prototypes don't match function
definition.
Merge pull request #179 from shemminger/v1.4.x-fixes

V1.4.x fixes
Cosmetic change to source header formatting
Added zconfig module

This saves and loads ZPL format text files. We use this already in FileMQ
for configuration, and I want to use it for CurveZMQ certificates as well.
The alternative is to use a flat file format like RFC 4716, but that does
not allow us to store multiple keys in one file, which would be useful
for authentication (e.g. server holding client long-term public keys in a
single file). ZPL is useful for any kind of configuration, so adding this
to CZMQ seems useful.

Note that this code originated in libzfl, and has lived for a while in
FileMQ (which will now use the zconfig class instead).
Methods to allow creation of private files
Using 'class' everywhere for consistency
Testing Travis CI
Regenerated source code to match headers
Fixed const on string options
Added cast from zmalloc, and STRONGER WARNINGS
Fixed name of Travis file
Merge pull request #178 from hintjens/master

Minor changes to support key management in zcurve
Disabled selftest on zcurve to patch broken master
Another attempt to fix Travis CI build
Merge pull request #180 from hintjens/master

Continuing work for Travis CI
Fixing yet more merge conflicts, gaaargh
Merge pull request #182 from hintjens/master

Merge conflicts
Added ldconfig after dependency builds
Added support for libsodium