Treating files as possible symbolic links on bundled file merges was
causing errors with temporary file cleanup later on. Since bundled
files are freshly unpacked and therefore not symlinks, we can feed them
directly to KDiff and avoid the issue.

The search order of the vanilla bundle folders was also tweaked so
patch bundles always take precedence.

Due to differences between the Steam and GOG versions of the game, the
previous case-sensitive search could miss some of the DLC folders.