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It used to return Maybe, now it always gives us a PackageIndex.
This depends on an API change in Cabal-1.9.x.

Not great but better than nothing.

Slightly experimental. We should look out for unexpected consequences.

And use exceptions rather than return codes.

Use the missing defaultInstallFlags.

See http://www.opensource.org/licenses/bsd-license.php

The stability field in .cabal files is deprecated since it's mostly useless.

Using hyphens rather than upper case.

We do not know if programs are installed or not so report
unknown rather than saying it is not installed.

We can no longer expect mtl, network and parsec to be installed.

The order of the package db stack is important.

This is an old non-standard extension that some tar tools still use.

Previously only created the immediate parent directory.
No rely more heavily on the file security check to make
sure we are not writing files outside of the target area.

When checking for tarbombs, ignore PAX entry types 'g' and 'x'.
These do not get extracted so their names do not matter.

Remove local copies. Also fixes a bug recently introduced
in the writeFileAtomic function, spotted by Peter Robinson.

The new cabal init stuff needs some work.