cast timestamps to strings before comparing for ruby 1.8, 1.9 compatibility

Author: cbeer

test/provider/models.rb

@@ -112,7 +112,7 @@ def generate_chunks(records, limit)
   end
 
   def generate_records(number, timestamp = Time.now.utc.xmlschema, sets = [], deleted = false)
-    @earliest = timestamp.dup if @earliest.nil? || timestamp.to_s < @earliest
+    @earliest = timestamp.dup if @earliest.nil? || timestamp.to_s < @earliest.to_s
     @earliest = timestamp.dup if @earliest.nil?
 
     # Add any sets we don't already have