Add a missing import in CPButton, and a test to ensure you can create one on the command line.

AppKit/CPButton.j

@@ -24,6 +24,7 @@
 @import "CGGeometry.j"
 
 @import "CPControl.j"
+@import "CPStringDrawing.j"
 
 #include "CoreGraphics/CGGeometry.h"
 

Tests/AppKit/CPButtonTest.j

@@ -0,0 +1,15 @@
+
+@import <AppKit/CPButton.j>
+@import <AppKit/CPStringDrawing.j>
+
+@implementation CPButtonTest : OJTestCase
+{
+}
+
+- (void)testCanCreate
+{
+    var button = [CPButton buttonWithTitle:"hello world"];
+    [self assertTrue:!!button];
+}
+
+@end