[Sparkle] New Checking Behavior

[Andy Matuschak]

Hey, all. I wanted to tell you about some new behavior I implemented  
for Sparkle's checking.

I recently realized that checking on startup behavior is basically  
equivalent to and better than a check interval of something like a  
day. So there's no more SUCheckAtStartup. Now it's all just check  
intervals. The default is a day, which will pretty much preserve  
whatever behavior you had before.

Also, I don't like the very first thing I see when I launch a new app  
to be "can I check for updates plz?". Sparkle won't ask for permission  
until the second launch now.

- Andy Matuschak