added ensure to show_file_extensions to avoid Finder restarts. (+1 squashed commit)
Squashed commits:
[d17ab28] added ensure to show_file_extensions to avoid Finder restarts.
fixed value type so ensure works.
trying to figure out how to avoid triggering killall Mail.
Revert "trying to figure out how to avoid triggering killall Mail."

This reverts commit f4f44d4a0a52e3568cf48628b2d044ae067582c1.