Bug 55884 Loading a user library from file does not warn when overwriting an existing library [build path]
Works in I2004032400010 + plug-in export for I200403240800 Add library 'mylib'. Save it. Change it. Load library from file. ==> should warn that 'mylib' gets changed.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/preferences/UserLibraryPreferencePage.java
/* (non-Javadoc)
		 * @see org.eclipse.jdt.internal.ui.wizards.dialogfields.IStringButtonAdapter#changeControlPressed(org.eclipse.jdt.internal.ui.wizards.dialogfields.DialogField)
		 */
		public void changeControlPressed(DialogField field) {
			String label= isSave() ? PreferencesMessages.getString("UserLibraryPreferencePage.LoadSaveDialog.filedialog.save.title") : PreferencesMessages.getString("UserLibraryPreferencePage.LoadSaveDialog.filedialog.load.title"); 
			FileDialog dialog= new FileDialog(getShell(), isSave() ? SWT.SAVE : SWT.OPEN);
			dialog.setText(label);
			dialog.setFilterExtensions(new String[] {"*.userlibraries", "*.*"}); 
			String lastPath= fLocationField.getText();
			if (lastPath.length() == 0 || !new File(lastPath).exists()) {
				lastPath= fSettings.get(PREF_LASTPATH);
			}
			if (lastPath != null) {
				dialog.setFileName(lastPath);
			}
			String fileName= dialog.open();
			if (fileName != null) {
				fSettings.put(PREF_LASTPATH, fileName);
				fLocationField.setText(fileName);
			}
		}
		private IStatus updateShownLibraries(IStatus status) {
			if (!status.isOK()) {
				fExportImportList.removeAllElements();
				fExportImportList.setEnabled(false);
				fLastFile= null;
			} else {
				File file= new File(fLocationField.getText());
				if (!file.equals(fLastFile)) {