Fix <rdar://problem/5609579> (DOMParser().parseFromString() freezes Safari when parsi...

Fix <rdar://problem/5609579> (DOMParser().parseFromString() freezes Safari when parsing large nodes with XML entities)
http://bugs.webkit.org/show_bug.cgi?id=16076

Reviewed by Maciej Stachowiak.

XMLTokenizer was calling CharacterData::appendData twice per entity in the fragment of XML being
parsed (once for text before the entity, once for the entity itself).  This triggered O(n^2) copying
of the CharacterData's string due to resizing.  We now prevent this happening by buffering all the
content for a given Text node in the XMLTokenizer before sending it out to the node in a single go.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@27936 268f45cc-cd09-0410-ab3c-d52691b4dbfc