fix mistaken references to OAI::ArgumentError (now OAI::ArgumentException)

Author: ndushay

lib/oai/client.rb

@@ -314,7 +314,7 @@ def parse_date(value)
       Date.parse(value) # This will raise an exception for badly formatted dates
       Time.parse(value).utc # Sadly, this will not
     rescue
-      raise OAI::ArgumentError.new
+      raise OAI::ArgumentException.new "unparsable date: '#{value}'"
     end
 
     # Strip out invalid UTF-8 characters.  Regex from the W3C, inverted.

lib/oai/provider/response.rb

@@ -94,7 +94,7 @@ def parse_date(value)
       Date.parse(value) # This will raise an exception for badly formatted dates
       Time.parse(value).utc #  -- UTC Bug fix hack 8/08 not in core
     rescue
-      raise OAI::ArgumentError.new
+      raise OAI::ArgumentException.new "unparsable date: '#{value}'"
     end
 
     def internalize(hash = {})