Tracking which ports were installed explicitly

[Joshua Root]

Andre Stechert wrote:
> Didn't see anything about counts of the implicit dependencies in the
> ticket or in this thread.  The states of a port are probably
> "explicitly installed", "implicit against 1 other port", "implicit
> against 2 other ports", etc., right?  Otherwise, you have the
> potential of setting the orphaned bit too early.  Also, the "explicit"
> bit should probably be independent of the implicit dependency count.

If it's done as proposed in the ticket, you would do 'port dependents
foo' (or rather its internal equivalent) to see whether foo is orphaned.
If it has no dependents, it's orphaned. Explicitly installing a port
adds 'world' as a dependent.

- Josh