Make getopts count (and thus align/paginate) in terms of codepoints not bytes.
Added note that there is still more to do on 5516.

Also added regression test for the byte vs codepoint issues that the
previous commit fixes.
char_len is more succinct than count_chars.
auto merge of #8710 : pnkfelix/rust/fsk-issue5516-codepoint-fix, r=alexcrichton

...bytes.

(removing previous note about eff-eye-ex'ing #5516 since it actually does not do so, it just gets us half-way.)