Update the configure logic for the new pmix120 component
ckpt
Get the pmix120 component to work - still not really registering or handling notifications, but infrastructure now operates
Cleanup some of the symbol scopes, and provide a more comprehensive rename.h file. Will pretty it up later - let's see how this works
Cleanup the rename files to use the pretty macros
NOTE: Building with external pmix *requires* that you also build with external libevent and hwloc libraries. Detect this at configure and error out with large message if this requirement is violated.
Closes#1204 (replaces it)
Fixes#1064
