NF: add empty tests package
TST: add a very crude test of self building
NF: add reown_mpkg command, add tests

Add command to post-process changing ownership of files in archives.
NF: option to install to sys.prefix for frameworks

For framework builds, the code forced the scripts and data to /usr/local
and /usr/local/share respectively. Add 'local-scripts' and 'local-data'
to override this and put scripts, data into the python tree instead.
Make a test script to check this is so.