db/distmap: pkgdir_make_distfile_volatile()

+ detailed exception messages
roverlay, apply_rules: check add-policy
packagerules: fix typo
distroot: do not create subdirs when renaming

replace os.sep in the repo name with "_" instead.
addition control: packagedir.add_package()

... implementation

This means that hand-written add-policy package rules are usable now.
cmdline, pkg/ebuild list file are still TODO.
addition control: rename force-add=>force-replace

There's no real "force-add".
addition control: add replace-only
addition control: logging
add-policy package rules: accept >=1 value(s)

The "force-deny","force-replace",... values get ORed.
Due to action precedence, only "force-deny" is effective even
if "revbump-on-collision",... are also set.
add COULDFIX note