Merge pull request #170 from danriegsecker/master

Corrected client expiry
Merge pull request #171 from danriegsecker/master

Removed reference to nonexistent server unique_id
Problem: String return values for API methods are not const
Solution: Make method and property getter sstring methods return const char *
Merge pull request #172 from jemc/master

Problem: String return values for API methods are not const
Add explicit cast to zhash_cursor calls

Problem: The zhash_cursor function returns const void * and the
zproto_codec_c assumes that it return const char *.

Solution: Add explicit cast to zhash_cursor calls.