Add validChanged(bool) to PathChooser.

This is useful when e.g. connecting directly to the setEnabled() slot of
a Widget.

src/libs/utils/basevalidatinglineedit.h

@@ -81,6 +81,7 @@ public:
 
 signals:
     void validChanged();
+    void validChanged(bool validState);
     void validReturnPressed();
 
 protected: