bootInfo uses boot.
bootInfo as API.
doc.
hcar.
changelog.
Generate ghc package.cache before running spec
Correct check-packageid/cabal.sandbox.config.in
Add some test data

..for testing behaviour with multiple versions/ids of packges being
available
Add package.cache to .gitignore and make .cabal-sandbox absolute
Add cabal file to `duplicate-pkgver` test data

It's not really valid but enough to make ghc-mod happy, without it
findCradle doesn't work properly and without the empty `library`
sections it crashes even.
Add test data to Extra-Source-Files