When playing PWADs with classic Doom, you always got the "this game has been modified" banner and had to hit enter to continue. If you played a lot of PWADs, you got used to hitting enter regularly. It became a core part of the Doom-playing experience. Even if you used one of those lovely launchers that came on the shovelware CDs which streamlined the PWAD choosing experience, you always had to hit the enter key.
This commit restores this classic behaviour and allows those who still have the muscle-memory "hit enter" behaviour permanently burned into their nervous systems to finally be at peace.
TODO for a future commit: the coloured top-line of text (red for 1.666, blue for 1.9 iirc)
Some feedback from IRC:
<Linguica> its funny because its nearly indistinguishable from real chocolate doom feature requests
<jmickle> i actually first thought "huh, kinda surprised this isn't in already
<ryan> best chocolate-doom feature yet!