There are a few changes in this patch:
 
   - New flag to register, --inplace.  "setup register --inplace"
     registers the package for use in the build tree, i.e. without
     installing.  It works with GHC only, currently.
     
   - The parameters to RegisterCmd, UnregisterCmd and InstallCmd are a
     legacy from before the time of hooks (or something) and don't
     serve any purpose any more, AFAICT.  So I removed them.
 
   - I don't think "setup register" worked propertly before if
     --user was given to configure.  It does now.

   - New flag to register: --with-hc-pkg (just the same as when
     given to configure, but lets you override it at register-time)