Add keyboard accessibility for buttons.

Fixes #1

content/resurrect-select-mirror.xul

@@ -29,7 +29,7 @@ window.addEventListener('load', resurrect.loadTarget, false);
     </radiogroup>
   </groupbox>
 
-  <groupbox id='resurrect' onclick='resurrect.clickedXul(event);'>
+  <groupbox id='resurrect' oncommand='resurrect.clickedXul(event);'>
     <caption label='&resurrect.fromMirror;' />
 
     <xul:button

content/resurrect.js

@@ -56,6 +56,8 @@ var resurrect={
       // Add event listener.
       contentDoc.getElementById('resurrect').addEventListener(
           'click', resurrect.clickedHtml, false);
+      contentDoc.getElementById('resurrect').addEventListener(
+          'keypress', resurrect.clickedHtml, false);
     }
   },
 
@@ -121,6 +123,10 @@ var resurrect={
     if ('true'==event.target.getAttribute('disabled')) {
       return;
     }
+    if ('keypress' == event.type) {
+      if (event.target.parentNode.id != 'resurrect') return;
+      if (event.charCode != 32 && event.keyCode != 13) return;
+    }
 
     return resurrect.clickHandler(
         event,