New improvements, changes and all the fish for 0.5.0.

New improvements, changes and all the fish for 0.5.0.

* Synced proplib code with NetBSD HEAD, which replaces the red-black
  tree implementation and checks for NULL pointers passed in to the
  _dict/_array functions.

* The _zfile functions in the API are now encapsulated into its own
  file, that way upstream changes are merged easily.

* The list of public API exported symbols is now handled via libtool's
  -exported-symbols option so that local symbols don't pollute the API.

* Explicitly require a C99 compiler. Don't want to waste time in non
  C99 compilers.

* Build with Stack Smashing Protection if supported by the compiler,
  and a bunch of compiler warnings.