1.5.16 bug with Reply-To - similar to ticket #2304

[Lars Hecking <lhecking@xxxxxxxxxxxxxxxxxxxxx>]

 Since I upgraded to 1.5.16, I'm observing some bizarre behaviour related to
 Reply-To. The situation is similar to the one described by Derek in
 #2304. Actually, I just found this in 1.5.15 as well, so who knows when
 the change actually occurred.

 Basically, I tried to reply to a ticketing system which has the Reply-To:
 set accordingly, but this gets ignored completely, and the reply goes to
 the To:. No setting of reply_to changes anything.

 But: this _only_ happens when hostname is set explicitly in .muttrc!

 Commenting out hostname isn't really an option, as I use it to masquerade
 my From: address. I guess my .muttrc hasn't changed much in years.