If you're using a manually named session (either through ':SessionSave
mysession', `:SessionSearch`, or `:SessionRestore mysession`) then we'll
now auto-save to that session on exit instead of always autosaving to
the session derived from the cwd.

When auto-saving, if the session has been manually named use that
session name instead of the cwd session name. Fixes manually named
session not auto-saving on exit.

Turn off auto_create to make sure correct session name is checked when
deciding to allow session saving or not