Reviewed by Darin Adler.

        More preparation for:
        <rdar://problem/6104369> Hitting return at the end of a quoted line creates an extraneous quoted line

        * editing/BreakBlockquoteCommand.cpp:
        (WebCore::BreakBlockquoteCommand::doApply): Added comments.  Don't need to use newStartNode.  If the 
        startNode needs to change, change it.  Afterwords, check to make sure that it hasn't left topBlockquote.  
        This is slightly stricter than before, where we just made sure that it still had a topBlockquote.  This 
        doesn't really fix a bug, since we can't really get into a situation where we move to a different 
        topBlockquote, but it simplifies the code.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@38004 268f45cc-cd09-0410-ab3c-d52691b4dbfc