Don’t autosave when the editor contains the focused element on focusout

This prevents autosave when things like the autocomplete menu are
opened.

Fixes #3
Fixes atom/autocomplete#46
Fixes saschagehlich/autocomplete-plus#16
Merge pull request #24 from atom/ns-suppress-when-still-contains-focus

Don’t autosave when the editor contains the focused element on focusout