[dialog addon] Select starting value when one is given

Closes #2866

Author: marijnh

addon/dialog/dialog.js

@@ -56,7 +56,10 @@
 
     var inp = dialog.getElementsByTagName("input")[0], button;
     if (inp) {
-      if (options.value) inp.value = options.value;
+      if (options.value) {
+        inp.value = options.value;
+        inp.select();
+      }
 
       if (options.onInput)
         CodeMirror.on(inp, "input", function(e) { options.onInput(e, inp.value, close);});