XPrompt: added ^A and ^E and more
XPrompt: added ^A and ^E and more

- added ^A (start of line) and ^E (end of line)
- added support for escaping spaces (see an example of it's use in the
  new ShellPrompt)
- some code cleanup: I'm now tracking changes to XPrompt also in
  modified version that supports i18n. This is the reason of some name
  changes.

darcs-hash:20071005112122-32816-797e755161388185fc2db63b03552f59632aca22

yzhou61/xmonad-contrib,yzhou61/xmonad-contrib,yzhou61/xmonad-contrib