mnemonic on Close button in ControlPanel Help dialog is not i18n'ed properly

In ControlPanel Help dialog, the mnemonic for "Close" button is being set to
the FIRST character of the resource string below. This is wrong i18n because
the character doesn't necessarily appear at the beginning of the l10n resource
string.

ext/plugin/java/src/sun/plugin/panel/ActivatorPanel.java:
line 331-

        JButton close = new JButton(mh.getMessage("help_close"));

        close.setMnemonic(close.getText().charAt(0));

        buttonPanel.add(close);

The mnemonic should be extracted into the l10n resource files ControlPanel_*.java by the same
way as the other buttons below.

        apply.setMnemonic(mh.getAcceleratorKey("apply"));