Improve `find` command for cd widgets: exclude proc/dev etc

When using the widget in "/", it would descend into 'dev/'.
Using '*' for the starting path would do so also with the new '-fstype'
excludes.

`cut -b3-` and `sed 1d` have been added to massage the different format
of the list.

This also uses `-L` with all calls to find, especially for the file
finders.

Ref: https://github.com/junegunn/fzf/pull/122