port archive should be smarter with regards to portarchivetype

[Lord-Kamina (Gregorio Litenstein)]

Currently, if you have a bunch of ports installed and then decide to change portarchivetype to something else; say tgz, port archive isn't smart enough to realize you changed that key. As a result, changing portarchivetype implies having to uninstall and rebuild all your ports.

There are at least two ways I can think of in which this could be fixed. One would be to just decompress the existing archives and recompress them in the desired format, another would be to use the registry to just create a new archive from the already installed files.