response#getWriter should throw UnsupportedEncodingException in case of bad character encoding used

[olamy]

TCK issue

response.setCharacterEncoding("allez-les-bleus");
then 
response.getWriter(); 

According to TCK and servlet api this should throws UnsupportedEncodingException
but actually EncodingHttpWriter catch it then wrap it in new RuntimeException

@gregw I was not sure how to fix that.
I would have preferred to change the constructor (to avoid such catch and instanceof block
public EncodingHttpWriter(HttpOutput out, String encoding)
to
public EncodingHttpWriter(HttpOutput out, String encoding) throws IOException

Signed-off-by: Olivier Lamy [email protected]

[gregw]

@olamy changing constructor to throw is fine. It is only used in 1 place.

[gregw]

LGTM