Bug 126705 [Preferences] FileFieldEditor does not call doCheckState
org.eclipse.jface.preference.FileFieldEditor does not call doCheckSate() during checkState() which makes it difficult to subclass this editor to perform additional checks like it is possible with StringFieldEditor
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/FileFieldEditor.java
* Creates a file field editor.
     * 
     * @param name the name of the preference this field editor works on
     * @param labelText the label text of the field editor
     * @param enforceAbsolute <code>true</code> if the file path
     *  must be absolute, and <code>false</code> otherwise
     * @param parent the parent of the field editor's control
     */
    public FileFieldEditor(String name, String labelText, boolean enforceAbsolute, Composite parent) {
        this(name, labelText, enforceAbsolute, VALIDATE_ON_FOCUS_LOST, parent);
    }
    /**
     * Creates a file field editor.
     * 
     * @param name the name of the preference this field editor works on
     * @param labelText the label text of the field editor
     * @param enforceAbsolute <code>true</code> if the file path
     *  must be absolute, and <code>false</code> otherwise
     * @param validationStrategy either {@link StringButtonFieldEditor#VALIDATE_ON_KEY_STROKE}
     *  to perform on the fly checking, or {@link StringButtonFieldEditor#VALIDATE_ON_FOCUS_LOST}
     *  (the default) to perform validation only after the text has been typed in
     * @param parent the parent of the field editor's control.
     * @since 3.4
     * @see StringButtonFieldEditor#VALIDATE_ON_KEY_STROKE
     * @see StringButtonFieldEditor#VALIDATE_ON_FOCUS_LOST
     */
    public FileFieldEditor(String name, String labelText,
            boolean enforceAbsolute, int validationStrategy, Composite parent) {
        init(name, labelText);
        this.enforceAbsolute = enforceAbsolute;