- fix http://bugs.webkit.org/show_bug.cgi?id=13227
          StringImpl::isLower incorrectly assumes islower returns 1 (it can return any non-0)

        * platform/StringImpl.cpp:
        (WebCore::StringImpl::isLower): Based on test application results, changed to use &&
        instead of trying to use & to avoid branches. Use U16_NEXT so we can handle characters
        outside the BMP. Improved comments.
        (WebCore::StringImpl::lower): Improved comments.
        (WebCore::equalIgnoringCase): Changed to use && instead of trying to use & to avoid
        branches. Improved comments. Added an assertion about the assumption we're
        making that characters in the char* are all ASCII.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20900 268f45cc-cd09-0410-ab3c-d52691b4dbfc