TODO list, most priority at the top.

[x] Problem of tarballs which disappear when package is updated
[ ] Solve issue of depending on a newer version of a base package than what is
    available in the currently installed version of R
[x] Do-not-process feature to list packages we shouldn't even look at
[x] Allow per-package keywords for:
    - packages which require e.g. 64 bit only
    - packages present in multiple repositories
    - ?
[x] Better way to deal with R suggestions
[x] Handle slots in fuzzy dependency resolver
[x] readline in depres_console