XPrompt: added comletion and history support
XPrompt: added comletion and history support

This is a long patch the brings us a real prompt, more or less: completions
now work. Added history support, with a configuration option: defaul history
size is 256.
defaultPromptConfig is now deprecated: please use defaultXPConfig instead

darcs-hash:20070803154531-32816-a2dfec51e8988173ef8b494e268a4418686658f9

jthornber/XMonadContrib,jthornber/XMonadContrib