port "cask" -- installing prebuilt binaries

[Ken Cunningham]

I've been building a few of these "cask" installers for my own use.

I'm finding using the normal port activate/deactivate process quite inefficient for this...

For example, SageMath is a 1.5GB dmg, and is about 4GB installed. Downloading the dmg, decompressing it and copying the contents into destroot, recompressing it, then activating it and decompressing it again takes just forever to do and seems wasteful on space as well.

A more efficient method that overrides activate/deactivate and does not needlessly de&re&decompress everything would seem useful.

Also a recommended method to avoid mirroring the distfiles ("NoMirror" license I presume) and not caching the archives (clearing archive_sites I suppose) are needed.

Ken