usr.bin/mail not SUSv3 compliant

["Douwe Kiela" <virtus@xxxxxxxxxx>]

Hello there,

The usr/bin/mail program is not SUSv3 compliant, the options that are
described within the standard and are not available in our version of the
program are:

-e Test for the presence of mail in the system mailbox. The mailx utility
shall write nothing and exit with a successful return code if there is mail
to read.
-F Record the message in a file named after the first recipient. The name is
the login-name portion of the address found first on the To:line in the mail
header. Overrides the record variable, if set (see Internal Variables in
mailx.)
-H Write a header summary only.

I was browsing around and found these options, so I decided to add them.
Before I started coding, I decided to check the other BSD's versions first.
And I found that FreeBSD's already implemented these options.

What I did in the following patch is the same as the FreeBSD version, with
some modifications by me. Furthermore I also went on removing the (void)'s
when I saw them in front of my editor cursor.

The patch can be found on my leaf account:
http://leaf.dragonflybsd.org/~virtus/mail.diff

I hope anyone has the time to commit this.

Greetings,
Douwe