Per request, add cross-project support to BBv1.

svn path=/branches/bbv1_cross_project/boost/tools/build/; revision=19929
Fix missing path when building from the root of a project.
Fix missing project name subpath for stage target.

svn path=/branches/bbv1_cross_project/boost/tools/build/; revision=19930
Fix project getting reset on subinclude.
Fix stage going to the bin location instead of the project location.
Fix fake target for stage not having plain ungristed name.
** Regression test now run.. but fail to get processed. **

svn path=/branches/bbv1_cross_project/boost/tools/build/; revision=19937