Add a generalised variant of 'topHandler'.
Don't die if some deps weren't reinstalled.
Use globalInstallDirs as the sandbox location.

Reverts 7b2e3630f2ada8a56bf9100144e1bb9acbe6dc6a. Instead of temporarily setting
'configUserInstall' to 'False' in various places, we now just check that we're
not in a sandbox when deciding whether we should use 'rootCmd'.
Add an '--only' flag for 'build', 'test' and 'bench'.

Allows to skip the automatic reinstallation of add-source deps.
Merge pull request #1327 from 23Skidoo/skip-add-source-check

Add an '--only' flag for 'build', 'test', 'bench' and 'run'.
init: generate build-depends with >=x.x && <x.y syntax instead of ==x.*

fixes #1329.
Add a function for reading the contents of a single package DB.

'getInstalledPackages' requires to pass in a 'PackageDBStack'.
Add a function for listing packages installed in a sandbox.
Make failReadE use the error message supplied