Strict testing of build dependencies

[m]

It would be pretty handy if the package build environment contained only its build dependencies and its build dependencies' runtime dependencies.

For example, say I wanted to build app-misc/foo. Portage might:

1. Look at app-misc/foo's build dependencies
2. For each build dependency,
   1. run equery f "${build_dep}" and add the results to a file list.
   2. look at the build dependency's runtime dependency
   3. For each runtime dependency
      1. run equery f "${runtime_dep}" and add the results to the file list
      2. (Recurse through runtime dependencies)
3. Construct a filesystem view for further build effort that, at least initially, presents only the files in the file list.

(To cope with circular dependencies, at some stage a set of bootstrap files will be necessary.)

This would force consistent build failures anywhere parallel emerge is subject to a race condition.

[Doug Freed]

This will be done in a separate project, as a replacement sandbox that can easily be configured such that only certain programs are allowed access to certain files. Switching to that alternate sandbox will be handled in #5, so marking this as a duplicate of that.

[Doug Freed]

Duplicate of #5.