Override the LayoutAlignment method in BStringView.

Left align StringViews using layout API by default falling back
to the alignment settings set by SetAlignment() only if
SetExplicitAlignment() is not used.

This way StringViews are left-aligned by default, can be changed
using the Layout API, and the pre-Layout API legacy method is used
as a fallback.

See this thread for details:
http://www.freelists.org/post/haiku-development/Can-we-make-BStringViews-MaxSize-BSizeB-SIZE-UNLIMITED-B-SIZE-UNSET-by-default

headers/os/interface/StringView.h

@@ -42,6 +42,7 @@ public:
 	virtual	BSize				MaxSize();
 	virtual	BSize				PreferredSize();
 	virtual	void				ResizeToPreferred();
+	virtual	BAlignment			LayoutAlignment();
 	virtual	void				FrameMoved(BPoint newPosition);
 	virtual	void				FrameResized(float newWidth, float newHeight);
 

src/kits/interface/StringView.cpp

@@ -13,15 +13,15 @@
 
 #include <StringView.h>
 
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
 #include <LayoutUtils.h>
 #include <Message.h>
 #include <View.h>
 #include <Window.h>
 
-#include <stdio.h>
-#include <stdlib.h>
-#include <string.h>
-
 #include <binary_compatibility/Interface.h>
 
 
@@ -199,6 +199,14 @@ BStringView::ResizeToPreferred()
 }
 
 
+BAlignment
+BStringView::LayoutAlignment()
+{
+	return BLayoutUtils::ComposeAlignment(ExplicitAlignment(),
+		BAlignment(fAlign, B_ALIGN_MIDDLE));
+}
+
+
 void
 BStringView::FrameMoved(BPoint newPosition)
 {