Turn on cross-document messaging support by default

 Turn on cross-document messaging support by default

 top level:

         Turn on cross-document messaging support by default

         Reviewed by Darin.

         * configure.ac:

 WebCore:

         Turn on cross-document messaging support by default

         Reviewed by Darin.

         * Configurations/WebCore.xcconfig:
         * WebCore.pro:
         * WebCore.vcproj/WebCore.vcproj:

 WebKitTools:

         Turn on cross-document messaging support by default

         Reviewed by Darin.

         * Scripts/build-webkit:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@30270 268f45cc-cd09-0410-ab3c-d52691b4dbfc