If an installed plugin has a .ghost extension, remove it before trying
to match the filename against the given regex. This makes functions that
take paths and functions that take regexes behave the same way for
ghosted plugins.
- Don't recursively check .ghost file extensions: plugin.esp.ghost.ghost
is not a valid plugin filename.
- Only add a .ghost file extension if the path that does not exist has
an unghosted plugin file extension.
Oliver Hamlet
