[xmonad] XPrompt.Shell feature requests

[lithis]

There are a couple things that annoy me about XPrompt.Shell:

1. When tab-completing a directory name, a trailing slash is
not automatically appended. Thus an additional keystroke is
required, unlike any other tab completion system I’m familiar
with (mostly those in bash and Vim).

2. Filenames in the pop-up tab-completion list are escaped.
This makes the names harder to read. Could the unescaped
filenames appear in the list and then be escaped after tab
is pressed as the string is copied into the prompt line?

I looked at the source, but only got as far as finding that
the completion is done via bash’s compgen builtin. I coudn’t
find in bash’s man page how to add slashes to the output of
compgen.