So we now have the complete set of commands in one tool.
This uses the new Command infrastructure to do two way conversion between
flags as strings and as a structured parsed form.

first step to shell command line completion

So don't bother making it a parameter

Use the new cabal command line handling infrastructure. Use proper flag types
rather than strings. 
Drop support for per-package command line flags as it was generally agreed to
be confusing.

Set preifx to the global default when the config file says to do a global install. This still doesn't work if --global is given on the command line. Print the complete config if verbosity >= verbose. Don't save prefix to the config file, since that means we will use the user default even for global installs.

It is now about half as much code, and uses fewer and simpler
functions and data types. The external interface is now much smaller,
which meant that I had to change quite a bit of other code.
I orignally wrote this in parallel with dons' clean-up changes,
and had to merge by hand since darcs went into mad exponential conflict mode.
I hope I didn't revert too many of dons' changes.

Removed the build-dep command. It has been been broken since we started to use configurations, and should be subsumed by the planned cabal-setup integration.

Added a config file. Removed the old serv.list file. Added dinstall directory command line arguments.

This is useful when you want to build a development version of something whose dependencies are available in Hackage. 

cabal-install: Output usage info for the right command when pasrsing the package name arguments fails.