Purge_line breaks .sdirs when it is a symlink

[jloh]

If you symlink the .sdirs file to use with something like dotfiles the _purge_line function breaks the symlink since it moves the file and recreates it

[jloh]

Apparently I can overcome this by setting my .sdirs within a environment variable to be somewhere that it doesn't have to be symlink'd. This is a good alternative and I'll have a crack at going down this path.

[jloh]

This method worked fine, not ideal however.