Rewrite `abbr` function

The usage is still the same, but it's a lot more robust, and also no
longer assumes $fish_user_abbreviations must be a universal variable.

This also fixes the unexpected error output when calling `abbr -a` with
no existing abbreviations.

Calling `abbr -a` with an abbreviation that already exists now silently
overwrites the abbreviation, just like `function` and `bind` do, instead
of complaining.

0 files changed, 0 insertions, 0 deletions