Add CLEAN-OP to ASDF?

E.M. Baringer's Arnesi library has an ASDF clean-op in its src/asdf.lisp
file (thanks to fe[nl]ix on #lisp for the pointer).  Is there any reason
this operation could not be imported into the core ASDF distribution?
Cleaning out old FASLs seems like a very nice thing to have.

I don't *believe* that the license terms would cause any problems; we
would just have to give credit to Marco.  But IANAL.

Best,
Robert

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