check for font open errors

[geekosaur]

This may not have been done because throwIfNull can't be used directly. A wrapper using coerce works, though. Prevents xmonad from dumping core in XMonad.Prompt.printPrompt if an invalid font is specified.

[geekosaur]

BTW, XMonad.Prompt and other consumers of this need to check for an exception now, or they'll still crash (just not with a core dump any more, and with a message in the session log). Possibly this can be done for everything in XMonad.Util.Font.

[slotThe]

LGTM

[geekosaur]

@liskin , as most recent maintainer, are we okay to bump the version and then make xmonad depend on it? Do you think we need a major version bump for anyone else who might be using it?

[liskin]

@liskin , as most recent maintainer, are we okay to bump the version and then make xmonad depend on it? Do you think we need a major version bump for anyone else who might be using it?

Yeah, bumping to 0.3.5 is definitely okay. Don't think it's worth bumping the major.

[liskin]

I pushed a further simplification but a rebase squashing these little changes would be preferred pre-merge.