This morning I realized that the bug fix that I mentioned in my last post had only been applied to oldstatus, so I set about the simple copy and paste job of applying the fix to HEAD. I compiled it, ran Gaim, then attempted to receive a test file. The transfer failed when it arrived in oscar_sendfile_connected(). After several minutes of investigating, I found that gaim_proxy_connect() and the underlying OS call to socket() were returning zero as the file descriptor. Since zero is reserved for stdin, I thought this was obviously wrong. And so I spend a little while trying to figure out why this had happened... six and a half hours to be more exact. Frazzled, I started Googling up sockets. This is what I found:

Socket() is returning descriptor as zero. Is this valid? 
 
No, your computer has inhabited by evil spirits and must be destroyed
quickly and completely in a fire built in front of the local police
station while you hop around it on one foot and waving your arms vigorously. 
 
 If you really want to be certain that the evil spirits are dispelled
 and do not follow you home and infect another computer, you should also
 be completely nude and repeatedly play Wagner's Ride of the Valkyries
 BACKWARDS (otherwise you may end up summoning more spirits! very very bad!)
 on a kazoo until there is nothing left of the computer but ash. 
 
 
 Now that you have done that: 
 
 The real answer is yes. A socket descriptor can be from 0 to N (N being
 dependent on the system / OS). The only reason many people do not see a
 return of 0 normally is that it is assigned to the stdin stream. If stdin
 is closed though, 0 will start popping up as a return value on both socket
 and accept calls. 

Going on the assumption that Gaim 2.0.0 had closed stdin, I looked around for what else could be causing the error. I then found 2 lines in aim_get_command() that made the same assumption I did, that a zero file descriptor was bad news. I commented out the offending lines, and the world was again right.