Add aria-describedby support

src/Select.js

@@ -48,6 +48,7 @@ const Select = React.createClass({
 		addLabelText: React.PropTypes.string,       // placeholder displayed when you want to add a label on a multi-value input
 		'aria-label': React.PropTypes.string,       // Aria label (for assistive tech)
 		'aria-labelledby': React.PropTypes.string,	// HTML ID of an element that should be used as the label (for assistive tech)
+		'aria-describedby': React.PropTypes.string,	// HTML ID(s) of element(s) that should be used to describe this input (for assistive tech)
 		arrowRenderer: React.PropTypes.func,				// Create drop-down caret element
 		autoBlur: React.PropTypes.bool,             // automatically blur the component when an option is selected
 		autofocus: React.PropTypes.bool,            // autofocus the component on mount
@@ -854,6 +855,7 @@ const Select = React.createClass({
 			'aria-haspopup': '' + isOpen,
 			'aria-activedescendant': isOpen ? this._instancePrefix + '-option-' + focusedOptionIndex : this._instancePrefix + '-value',
 			'aria-labelledby': this.props['aria-labelledby'],
+			'aria-describedby': this.props['aria-describedby'],
 			'aria-label': this.props['aria-label'],
 			className: className,
 			tabIndex: this.props.tabIndex,

test/Select-test.js

@@ -3803,6 +3803,19 @@ describe('Select', () => {
 					'to contain', <input role="combobox" aria-labelledby="test-label-id" />);
 			});
 
+			it('passes through the aria-describedby prop', () => {
+
+				instance = createControl({
+					options: defaultOptions,
+					value: 'one',
+					'aria-describedby': 'test-label1-id test-label2-id'
+				});
+
+				expect(instance,
+					'to contain', <input role="combobox" aria-describedby="test-label1-id test-label2-id" />);
+			});
+
+
 			it('passes through the aria-label prop', () => {
 
 				instance = createControl({