documentation build button is broken

Originally reported by lvh (<http://twistedmatrix.com/trac/ticket/3923>).

When I press F7 in emacs (Twisted-dev minor mode enabled) to generate documentation, I get errors like this:

~/sandbox/twisted/positioning/doc/howto/: no such directory

I've been told that package/doc/howto is where docs used to go way-back-when, but this isn't the case anymore.

I'm not entirely sure how to fix the implementation, since I'm not sure what the function f : packageName, moduleName -> documentationDirectory *is* supposed to look like. For my project, it's probably the package name (positioning), for 90% of the modules it's probably the module name.