Bugfixes.

    * new/virtual-targets.jam (virtual-target.root): New rule
        (traverse): Don't traverse past roots.
    * new/targets.jam (main-target): Call 'virtual-target.root' as
        appropriate.


[SVN r15773]

tools/build

@@ -1 +1 @@
-Subproject commit 4115276dec781ead96d146da4d8bb7da90c00fe9
+Subproject commit 9e696814a3a7d9f0e1ef4ce55df8b718e1068167