<rdar://problem/4172984> KWQExceptions needs to use @try/@catch instead of relying on NSException.h internals

        Needed to undef try/catch because of 4333439.  Moved the
        declarations of variables that are returned from within a @try
        block outside the @try block (because of "might be clobbered by
        a longjmp or vfork" warnings).  Moved some return statements
        inside the @try block to fix volatilization errors with gcc4.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@11695 268f45cc-cd09-0410-ab3c-d52691b4dbfc