[bug-mailutils] showenvelope lacks newline

[積丹尼 Dan Jacobson]

On (info "(mailutils) Mail Variables")
'showenvelope'

     Type: Boolean
     Default: Unset

     If this variable is set, the 'print' command will include the STMP
     envelope in its output.


Alas showenvelope is defective, gluing the result to the front without a 
newline:

$ echo test|mail $USER
$ echo -e set showenvelope\\np 1\\nx|mail.mailutils --nosum|head -n 1
>From (null) Tue Dec 25 14:28:23 2018Return-path: <address@hidden>
$ mail.mailutils --version
mail.mailutils (GNU Mailutils) 3.5