* A direct tag-to-tag relationship can now be established between two things,...

* A direct tag-to-tag relationship can now be established between two things, which allows event lines to be properly setup between them. This is intended for interpolation and patrol specials which are linked via a shared tag, instead of an argument. A POSITIVE value represents the parent thing, where a NEGATIVE value represents the child thing.
* Added interpolation and patrol point specials to the persistent event line processing