"filterdiff -x ./some/file" does not remove changes for some/file.
We must be more careful about constructing the path name and
only add the prefix when it really means a directory.
While at it, also better normalize the path in copy_selected_files()
early on, to handle double slashes. Useful should the function ever
gets used for something other that dest_dir (which gets normalized in
sanity_check()).
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
