Add a way to cycle only through matching history entries in X.Prompt
Add a way to cycle only through matching history entries in X.Prompt

Ignore-this: d67aedb25f2cc6f329a78d5d3eebdd2b

This patch adds a way go up through X.Prompt's history using
only those entries that start with the current input, similar
to zsh's `history-search-backward'.

darcs-hash:20100113233036-7f603-e35d5dffbccfa6220ff8d387e84dc2ba95b7d2da

jthornber/XMonadContrib,jthornber/XMonadContrib