[oe] Recipes relation tree

[Frans Meulenbroeks]

It would also be nice to be able to get the used by information.
E.g. if I change a package (especially wrt staging) I would like to
verify that the packages which use the modified package still build.

The current el-cheapo solution for a package XYZ is to do something
like a grep  DEPENDS.*XYZ */*.bb but of course that won't work if
DEPENDS spans multiple lines.

FM