Reviewed by Maciej Stachowiak.
        
        Fixed http://bugs.webkit.org/show_bug.cgi?id=15490
        Iteration statements sometimes incorrectly evaluate to the empty value 
        (KDE r670547). 
        
        [ Broken off from http://bugs.webkit.org/show_bug.cgi?id=14868 ]
        
        This patch is a merge of KDE r670547, with substantial modification 
        for performance.
        
        It fixes do-while statements to evaluate to a value. (They used
        to evaluate to the empty value in all cases.) 

        It also fixes SourceElementsNode to maintain the value of abnormal 
        completions like "break" and "continue."
        
        It also re-works the main execution loop in SourceElementsNode so that
        it (1) makes a little more sense and (2) avoids unnecessary work. This 
        is a .28% speedup on command-line JS iBench.

        * kjs/nodes.cpp:
        (DoWhileNode::execute):
        (SourceElementsNode::execute):

LayoutTests:

        Reviewed by Maciej Stachowiak.
        
        Layout tests for http://bugs.webkit.org/show_bug.cgi?id=15490
        Iteration statements sometimes incorrectly evaluate to the empty value 
        (KDE r670547)        

        * fast/js/do-while-expression-value-expected.txt: Added.
        * fast/js/do-while-expression-value.html: Added.
        * fast/js/while-expression-value-expected.txt: Added.
        * fast/js/while-expression-value.html: Added.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@26617 268f45cc-cd09-0410-ab3c-d52691b4dbfc