Refactorings.

* build/project-roots.jam (load): Return object, not project root module
* build/project.jam (initialize): Renamed 'project-root-modue' attribute to
 'project-root'.


[SVN r23017]

tools/build

@@ -1 +1 @@
-Subproject commit 877eb5801a722077cb86c35ff956a2f8d88ecad9
+Subproject commit 8375c3d5dc3b7c65f5eb4fcd1729d9bafdc95aa2