Revert "make label location strategy work with unescaped strings"

This reverts commit 4daf037146.

This was causing failures in the Weplay selenium suite, where we
we're using partial matches. For example:

  fill_in "Write a message", ...

When the markup was:

  <label>Write a message to Bryan ...</label>

lib/webrat/selenium/location_strategy_javascript/label.js

@@ -1,7 +1,8 @@
 var allLabels = inDocument.getElementsByTagName("label");
 var candidateLabels = $A(allLabels).select(function(candidateLabel){
+  var regExp = new RegExp('^' + locator + '\\b', 'i');
   var labelText = getText(candidateLabel).strip();
-  return labelText.toLowerCase() == locator.toLowerCase();
+  return (labelText.search(regExp) >= 0);
 });
 if (candidateLabels.length == 0) {
   return null;