This commit adds the capability to specify a whole directory which
contains data-files in a project's .cabal file.
If a data-files entry ends with a slash, like "static/", then it will
pull in all files under the directory named "static/".
* This has only been tested by calling matchDirFileGlob in GHCi.
* I'm not sure about the name (data FileGlob = DirTrailingSlash --
perhaps it should have Glob on the end like the others?) but I've been
unable to come up with anything better.