nnpkg: streamline looking for configures
nnpkg: get_root_path (new name for get_root)
nnpkg: stay in package root

From now on ensure, and assume that we are running in the package root.
For out-of-tree builds, more support needed.
nnpkg: prepare for out-of-tree builds

Still assume everything runs from the package root, except the commands,
which can switch to a different directory (and create if it does not exist).
If it needs to create it, it will show this creation and changing.
For our code, we still assume we are in the package root, and restore after the command.
nnpkg: allow out-of-tree builds

To use different directories, we need to tell grep_all where to look for the files
for the generated files (typically makefile), which will be in the builddir
relative to the package root.  For the configure stuff, we will need to re-compute its
path in the package root relative to the build dir however.
nnpkg: compute use_dir only once
nnpkg: more packages