Non-string system dependencies

[mtstickney]

I've just noticed that in the latest quicklisp release, the cffi-toolchain system depends on the system (:VERSION "asdf" "3.1.2"), which breaks qlot's ensure-installed-in-local-quicklisp. ensure-installed-in-local-quicklisp tries to string-downcase the system name, which in this case is a list rather than a string.

I'm not quite sure what the fix is here. Supporting versioned dependencies would mean coming up with some sort of versioned object to pass to ql-dist:ensure-installed -- there are other issues with versioned systems, but I think that's quicklisp/asdf's problem. Things might be trickier if the dependency is coming from a non-quicklisp system pulled in by qlot, though.