In Cssablanca, the letters of transit were signed by Vichy General Weygand, not Free French General de Gaulle. Listen to the soundtrack carefully.
Well, I've just listened to the soundtrack carefully, and I have to say, I still hear Peter Lorre saying "General de Gaulle", not "General Weygand". Now, both names will sound somewhat similar in the proper French pronunciation, but not exactly alike, and after replaying that sequence about eight times, I'm still hearing a distinct 'D' sound from Lorre (the 'de' in 'de Gaulle'), as opposed to a 'W' for 'Weygand'. This is a bit more tenuous, but I also don't see Lorre's lips moving in a way that suggests a 'W'. The lips don't need to move at all from the last syllable of 'General' to 'de', where they would have to purse slightly to form the 'W' sound in moving from 'General' to 'Weygand'. I don't see his lips move at all, which also suggests to me that he's really saying 'de Gaulle'.
Searching out the film's shooting script isn't terribly helpful, since the film's script wasn't even finished when the film started shooting and hasty rewrites were the order of the day, right up until the shooting of the final scene. I will note that Casablanca's Wikipedia entry indicates that Lorre says 'de Gaulle' and is subtitled in English on the DVD in the same way, while the French DVD subtitles say 'Weygand'. (I haven't checked this.) Also, the book Casablanca: Behind the Scenes indicates that the line references de Gaulle and makes no mention at all of Weygand.
So, absent more conclusive evidence, I'm sticking with my original hearing of the line. But hey, why take my word for it? You be the judge! Here's the scene from the movie; the specific line of dialogue in question comes at about the 1:45 mark.
Next week, we'll discuss whether or not Mark Hamill accidentally shouts "Carrie!" at the end of A New Hope. (Personally, I've always heard his shout as a meld of "Hey!" and "Yeah!". But we can hash that apart another time. Yay, obsessive movie geekery!)