[HtmlUnit] patch for req id.716568

[Noboru S. <sh...@le...>]

req id 716568:HtmlPage.loadExternalJavaScriptFile ignore page encoding.

I made a patch for this problem.
(Sorry, this patch includes the changes for req id 721008.)

the changes are:
in HtmlPage.loadJavaScriptFromUrl:
   it compare the encoding of response for script file and the enconding
   of refering page.
   if the response encoding is ISO-8859-1 (this means default encoding 
   and the server might not send charset in content-type header) and
   the page encoding is not ISO-8858-1 (this means the encoding was 
   sent in response header or declared in meta tag), the response body
   of script file will be re-read with the encoding of refering page.
WebResponse, HttpWebConnection:
  added the features related to get encoding information.

this is not the best solution.
For example, HttpWebConnection is now depending on HttpMethodBase.
this is not recommended way to use.
But anyway,
this works for me.