"cabal paths" command

A common question in #haskell on freenode is where package files are located. It varies by OS and by which database a package is installed in.

Something built into cabal that lists the current global, user, and sandbox directories would make this question much easier to answer.

No file or test is named. Start by inspecting Cabal's command-line entry points and the existing handling of global, user, and sandbox package locations. Done means a cabal paths command reports those directories across the supported installation databases and has coverage for its output.

Written by the indexing model from the issue text.