Make `#file_for` respect behavior of simple globs

Make `Projections#file_for` respect the behavior of simple (`*`, no
`**`) globs by replacing the `*` with `**/*` when it's at a path
boundary. when it's at a path boundary.

This fixes #10
Merge pull request #13 from glittershark/gh/10/prj_list_basic_globs

Make `#file_for` respect behavior of simple globs