help output: more gnu like output

First, the -J/--remote-header-name was wrongly sorted in the --help
output as pointed out in bug report #3349271.

Then, I changed the format of the texts to follow the man page better in
that it now uses "-A, --long" intead of "-A/--long". I also made all
additional arguments get written as in "-A, --long FILENAME" instead of
the previous "<filename>" style.

Reported by: Herve Amblard
Bug: http://curl.haxx.se/bug/view.cgi?id=3349271