allow composing a breve also with lowercase u

The first patch allows composing ĕ, ğ, ĭ and ŏ also with a lowercase u (instead of only with an uppercase U as is currently the case). The letters ă and ŭ can already be composed with a lowercase u, so this patch harmonizes things.

The second patch adjust two comments about the APL compose sequences that were invalidated by a commit some eight years ago.