changed result type to const char* instead of char*
Merge pull request #415 from ksergey/zsocket_type_str

changed result type to const char* instead of char*
Merge pull request #417 from hintjens/master

Fixed erroneous check for OS/X
Removed PRINTF validation from man pages

- was mucking up man page contents
- moved to end of header file, outside API section
- simplified macros in czmq_prelude.h