Bug 73083 [Encoding] Need to verify encodings and indicate unavailable ones
When the encodings are set up we need to ensure that they are in the list of valid encodings available from the VM. Those that are not should be indicated as such and not be selectable in the UI.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/ide/dialogs/AbstractEncodingFieldEditor.java
* @return String
	 */
	protected String defaultButtonText() {
		return IDEWorkbenchMessages.format(
				"WorkbenchPreference.defaultEncoding", new String[] { defaultEnc });
	}
	/**
	 * Populate the encodings combo. Set the text based on the
	 * selectedEncoding. If selectedEncoding is null set it to the
	 * default.
	 * @param encodings
	 * @param selectedEncoding
	 */
	private void populateEncodingsCombo(List encodings, String selectedEncoding) {
		String[] encodingStrings = new String[encodings.size()];
		encodings.toArray(encodingStrings);
		encodingCombo.setItems(encodingStrings);
		if (selectedEncoding == null)
			encodingCombo.setText(getDefaultEnc());
		else
			encodingCombo.setText(selectedEncoding);
	}
	private void updateEncodingState(boolean useDefault) {
		defaultEncodingButton.setSelection(useDefault);
		otherEncodingButton.setSelection(!useDefault);
		encodingCombo.setEnabled(!useDefault);
		updateValidState();
	}
	private void updateValidState() {
		boolean isValidNow = isEncodingValid();