I was going to reimplement path resolution in ShellExecute, but half way through I realized that's very unnecessary.
Since what I wanted is a version of `PathResolve` that behaves differently _only_ for filespec paths, I ended up duplicating a lot of code, then I realized I can still pass filespec paths onto `PathResolve` and only deal with non-filespec paths.
-- v2: shell32: Fix ShellExecute for non-filespec paths.