More detail in SYSTEM-DIFFERENCES.

Systems that are removed now show the release in which they
appeared. It's easier to use failtail that way.
Handle known cases of ASDF dependencies as lists.

Also, signal an error on unknown cases so no weird new stuff slips
through.
Minor RECRANK-TO-FILE update.

Pass all args along to RECRANK.
Add some dist sanity checking.
Create dependency indexes that work around slashed system names.
Signal an error on mixed-case system file names.
Preload more SBCL things. I think.

This should be reworked, since some systems don't have correct
SB-<whatever> dependency declarations. They shouldn't be baked into
system-file-magic and depcheck.