That is, limit the ending `raco setup' to the same collections
as the corresponding `raco pkg install' (droppping collections
that no longer exist afterward, of course).
Make the installed-package database lock reentrant, change some
functions to take the lock, and fix the documentation on when a
lock is expected to be taken outside of functions.
Adds `pkg/pnr-db', `raco pkg index-copy', and `raco pkg index-show'.
Includes tools to build a database of modules that are supplied by
packages, which will be useful for a tool to recommend package
installs when a module is not found.
Also, document `pkg/lib' and add extra helper functions
for getting package information from a package name resolver.
