Fix #541: Line numbers resize when getting a new document

RSyntaxTextArea/src/main/java/org/fife/ui/rtextarea/AbstractGutterComponent.java

@@ -110,10 +110,26 @@ private static Listener getListener() {
 	 * Implementations can take this opportunity to repaint, revalidate, etc.
 	 *
 	 * @param e The document event.
+	 * @see #handleDocumentUpdated(RDocument, RDocument)
 	 */
 	abstract void handleDocumentEvent(DocumentEvent e);
 
 
+	/**
+	 * Called when the document is updated. This happens when an application
+	 * calls {@code textArea.read(reader)}, for example.<p>
+	 *
+	 * The default implementation does nothing. Subclasses can override.
+	 *
+	 * @param oldDoc The old document, which may be {@code null}.
+	 * @param newDoc The new document, which may be {@code null}.
+	 * @see #handleDocumentEvent(DocumentEvent)
+	 */
+	void handleDocumentUpdated(RDocument oldDoc, RDocument newDoc) {
+		// Do nothing
+	}
+
+
 	/**
 	 * Called by the constructor before the text area is set.  This is a hook
 	 * to allow subclasses to do any needed initialization.  The default

RSyntaxTextArea/src/main/java/org/fife/ui/rtextarea/Gutter.java

@@ -1260,6 +1260,11 @@ else if ("document".equals(name)) {
 				if (newDoc != null) {
 					newDoc.addDocumentListener(this);
 				}
+				for (int i=0; i<getComponentCount(); i++) {
+					AbstractGutterComponent agc =
+						(AbstractGutterComponent)getComponent(i);
+					agc.handleDocumentUpdated(old, newDoc);
+				}
 			}
 
 		}

RSyntaxTextArea/src/main/java/org/fife/ui/rtextarea/LineNumberList.java

@@ -250,6 +250,15 @@ void handleDocumentEvent(DocumentEvent e) {
 	}
 
 
+	/**
+	 * Overridden to update the width of this component.
+	 */
+	@Override
+	void handleDocumentUpdated(RDocument oldDoc, RDocument newDoc) {
+		updateCellWidths();
+	}
+
+
 	@Override
 	protected void init() {