Major property-manager rewrite, using const char * throughout

Major property-manager rewrite, using const char * throughout
interface instead of string.  This will result in a lot more
efficiency later, once I add in a simple hash table for caching
lookups, since it will avoid creating a lot of temporary string
objects.  The major considerations for users will be that they cannot
use

  node->getName() == "foo";

any more, and will have to use c_str() when setting a string value
from a C++ string.