display file icons before attempting to load Quick Look previews

[skurfer]

As discussed in #1552, attempting to load Quick Look previews before giving up and showing the file's icon instead introduced a noticeable delay. I changed it to show the file's icon (if it exists) first. The obvious downsides are the extra work of loading two icons, and sending two notifications. But loading the file's icon is usually lightning quick. (Almost no one complained about it when it was done on the main thread.) And if there is no Quick Look preview, the second notification never happens.

[skurfer]

So if we can merge this guy, I think it's time for another pre-release.

Do we want to move 32-bit plug-ins to a disabled folder or something? I don't think it would make a difference for #1546, but it might help some things. Also, I'm wondering if we should call this 1.1.0 instead of 1.0.1, since there's a break with backward compatibility.

[pjrobertson]

Moving disabled plugins to a separate folder isn't a bad idea. Seems Alcor did this before (but for all the plugins) - this used to be in QSController:

            if (lastVersion < [@"2000" hexIntValue]) {
                NSFileManager *fm = [NSFileManager defaultManager];
                [fm moveItemAtPath:QSApplicationSupportSubPath(@"PlugIns", NO) toPath:QSApplicationSupportSubPath(@"PlugIns (B40 Incompatible) ", NO) error:nil];
                [fm moveItemAtPath:@"/Library/Application Support/Quicksilver/PlugIns" toPath:@"/Library/Application Support/Quicksilver/PlugIns (B40 Incompatible) " error:nil];
            }

Maybe in the try/catch/throw code for plugin loading we could move disabled 32 bit plugins somewhere else. It'd clean up the Console a bit as well (on launch)