- Don't require `cl' when compile time.

- Don't require `cl' when compile time.
- Don't require `emu'.
- Require `pcustom' instead of `custom'.
- Add autoload setting for `mu-bbdb-get-prefix-method',
  `mu-bbdb-get-prefix-register-method' and
  `mu-bbdb-get-prefix-register-verbose-method'.
(mu-cite-default-methods-alist): Add setting for
`mu-bbdb-get-prefix-method', `mu-bbdb-get-prefix-register-method' and
`mu-bbdb-get-prefix-register-verbose-method'.
(mu-cite-get-field-value): Add DOC-string.
(mu-cite-get-ml-count-method): Add DOC-string; use `if' instead of
`when'; use `match-string'.
(mu-cite-get-value): Add DOC-string.
(char-category): New function.
(fill-cited-region): Add DOC-string.
(compress-cited-prefix): Add DOC-string.