Bug#458371: warn better about --all-locales

[jidanni@jidanni.org]

Package: libc6
Version: 2.7-5
Severity: minor
File: /usr/share/man/man1/locale.1.gz

Just saying

       -a, --all-locales

               Write names of available locales.

without as much as an asterisk to guide one's eyes to the fine print
at bottom,

       This representation is recommended over --all-locales one, due
       being the system wide supported values.

leads to embarrassments like in bugs 456463, 354278.

If you cannot change the program's output, then at lest warn better on
the man page and --help!