Refactorings.

* build/virtual-target.jam
  (clone-action): New rule.

* tools/stage.jam
  (stage-exe-generator.run): Use 'clone-action'.


[SVN r20647]

tools/build

@@ -1 +1 @@
-Subproject commit 190f723ba30b1e3d24d3c730087a9bd5d8d83842
+Subproject commit 5d76c845974c4d59f2a1419ae11ecbaa23562c34