Fixed #398
Deprecated zmsg_push by zmsg_prepend

- method was unsafe, taking ownership of the frame (and destroying it)
  without nullfying the reference.
- deprecated zmsg_push (and also zmsg_wrap which has same issue)
- added new zmsg_prepend () using safe API style

Cause of this change was 2-3 hours lost in zproto tracking down obscure
bug caused by use of zframe_push(). Once is enough. :)
VS 2013 (v120) solution and projects, x86/x64, static/dyanamic, debug/release.
Remove export define limitation that prevented a windows DLL from loading the library statically. Adapted snippet from libzmq.
Provide empty definition of CMQ_EXPORT for non-_WIN32 systems.
Change user of _WIN32 to __WINDOWS__ for consistency with existing impl. Fix static builds preproc instruction.
added zcert_save_secret() to documentation.
Merge pull request #399 from hintjens/master

Fixed #398
Generate VS2013 projects from GSL model. Remove filters files. Update GSL script to include new model. Update test project as dependency of czmq project. Fix static props for test project so that it properly correlates to all czmq buils.
Merge pull request #401 from evoskuil/master

VS 2013 (v120) solution and projects.