- implement String::createCFString

        * WebCore.xcodeproj/project.pbxproj: Added StringImplMac.mm and StringMac.mm.

        * bindings/objc/DOMInternal.mm: Moved NSString conversion functions out of here.

        * platform/mac/StringImplMac.mm: Added. Moved NSString conversion members here
        and added the CFStringRef ones.
        * platform/mac/StringMac.mm: Added. Ditto.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@15614 268f45cc-cd09-0410-ab3c-d52691b4dbfc