Assigning to Element.prefix should throw exception when using illegal characters

Assigning to Element.prefix should throw exception when using illegal characters
https://bugs.webkit.org/show_bug.cgi?id=76589

Reviewed by Eric Seidel.

This patch fixes a FIXME and implements the INVALID_CHARACTER_ERR
exception described in
http://www.w3.org/TR/DOM-Level-3-Core/core.html#ID-NodeNSPrefix

Tests: fast/dom/Element/prefix-setter-exception.html

* dom/Node.cpp:
(WebCore::isValidNameStartCharacter):
(WebCore::isValidNameCharacter):
(WebCore::hasInvalidValidNameCharacters):
(WebCore::Node::checkSetPrefix):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105388 268f45cc-cd09-0410-ab3c-d52691b4dbfc