Key view loop fixes/improvements

- Removed unnecessary code at beginning of CPTextField -becomeFirstResponder that might have been a hack to get around a bug I fixed.
- Fixed race condition in setTimeout closure in CPTextField -becomeFirstResponder.
- CPWindow -setInitialFirstResponder now works reliably and follows Cocoa behavior in that if -makeFirstResponder is called with something other than the window before the window is first shown, it will override the initial first responder.
- Like Cocoa, until the first responder is set during window load, the first responder is the window by default, not the content view.
- Optimized search for any view that has a previous/next key view set.
- Sheets can become key windows again.
- CPWindow -recalculateKeyViewLoop now just marks the loop as dirty, per Cocoa docs.
- CPWindow -autorecalculatesKeyViewLoop now behaves per Cocoa, it only has an effect when views are added or removed.
- If the first responder does not have a valid previous/next key view, it does not resign to nil, per Cocoa behavior.
- Code optimization and cleanup.
- Test app (KeyViewLoopTest) that demonstrates various scenarios.

Tests/Manual/KeyViewLoopTest/KeyViewLoopTest.xcodeproj/project.xcworkspace/contents.xcworkspacedata

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Workspace
+   version = "1.0">
+   <FileRef
+      location = "self:KeyViewLoopTest.xcodeproj">
+   </FileRef>
+</Workspace>