Allow 'standalone' projects.

* new/project.jam
  (inherit-attribute): New rule, extracted from 'initialize'.
  (initialize): Allow 'jamfile' parameter to be empty, in which case
    the project is 'standalone'.


[SVN r18544]

tools/build

@@ -1 +1 @@
-Subproject commit f9e4d0f7b8d098fc83f179cdb46a914f518e3561
+Subproject commit fd6016b3cd0606bdf65a6103656b7eb166ba571c