Fix a bug steve noticed when handling nested rewrites. We now turn this:

    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

into:

    NSAutoreleasePool * pool = objc_msgSend(objc_msgSend(objc_getClass("NSAutoreleasePool"), sel_getUid("alloc")), sel_getUid("init"));

instead of:

    NSAutoreleasePool * pool = objc_msgSend(objc_msgSend(objc_getClass("NSAutoreleasePool"), sel_getUid("alloc")), sel_getUid("init"))utoreleasePool"), sel_getUid("alloc")) init];

llvm-svn: 43347