fix(recursiveDelete): Handle symlinked folders correctly

[joshtrichards]

#184 added some handling for symlinks in recurseDelete() but only for files, not directories.

We don't use recursiveDelete() is many places where this is likely to happen currently, but since isDir() resolves/matches on symbolic links it's possible we would rmdir() (and so against the getRealPath()) rather than unlink() it. This would result in trying to:

• run rmdir() against a symlink
• run rmdir() against the same target more than once

We use recusriveDelete() to:

• reset the downloads directory (unlikely to be a problem here)
• reset the shipped apps directory (could be a problem here, but probably not very common admittedly)
• reset the themes example directory (could be a problem here, but no

[come-nc]

Needs to be adapted to #516 , but I think this is still valid.