ref #574

ref #574

Required for provides support as package might be pulled in via
non-primary package name. This allows relatively easily to pass
through inherited flags via the provided names. ref #574.

Reasoning:
- it is less useful now that we do not do common dependency merging
- provides support would make the required logic overly complicated
- callgrind reports that depending on the case it can improve or
  decrease performance (the overhead pays off only in some cases);
  the difference is not large either way

implementation is still not near finished, but now at least it
can handle it to a minimum degree. many cases are not done right
yet, though. ref #574.

in preparation for provides support. implements also some
dependency satisfaction helper routines.

ref #574.

* take list of tests to run (and default to all)
* merge the awk invocation to a function

Otherwise we might start to change packages unexpectedly when not
upgrading. This also fixes some other things the solver might've
decided to do.

Add also few test cases to detect bad behaviour.

ref #574

Will use 'p' for provides.

fixes #1010

also merge the expected output to the *.test files.

This we use proper arch in case modifying chroot installation.

In case someone prefers extra quesions while running apk in a
terminal. The file is always from the real root; not from --root
so that we will not accidentally enable interactive mode when in
initramfs bootstrap.

fixes #607.

audit is now mostly rewritten for the new functionality. And
has new features like --check-permissions, --recursive and
--packages.

$ROOT/etc/apk/protected_files.d/*.list can now contain additional
protected paths, one path per line:

+etc
@etc/init.d
-tmp

+ will include the directory as protected configuration directory.
@ considers the directory protected, but will backup only symlinks.
- removes any protection

lbu should be modified to put include and exclude paths in
etc/apk/protected_files.d/lbu.list. Additionally, some packages
might provide their own listings.

E.g. ssh might want to provide ssh.list with something like:
+root/.ssh
+home/*/.ssh

Load additional repositories from $ROOT/etc/apk/repositories.d/*.list
unless --repositories-file is given as parameter.

care is needed to get the score right.

In case someone did "fix --force" for package for which we have no
APK available, we would uninstall the package instead of silently
ignoring the request. This could mean worse things.

So now we just consider unavailable packages a bad deal for reinstall
requests. And will downgrade if necessary. But if we really don't
have any APK available, we just skip the request but report it.

Just in case same repository is mentioned with different tags.

If n+1 packages depend A, and A depend on B. Add n+1 dependencies
to B. Otherwise if someone conflicts B, B might be left out.

Leaving package unassigned is no longer a non-preferred action,
this fixes the final test case that was failing.

And with --force we might even install that scenario.
Add also some debug checks.

callgrind says it's more overhead than improvement. back jumping
effectively prunes all bad trees. but can be added later if it
becomes needed; due to e.g. provides support.

It is faster to just scan the cache directory for existing packages
at startup than trying to faccessat() them on demand. It also makes
quite a few parts of the code more readable and simpler.

* properly do absolute scoring now, the previous scoring where
  preference could get reduced could have caused incorrect early
  pruning of search tree

* backtracking is now separated from package state, and first
  branching point is the decision if a name is left unassigned
  or if something _has_ to be assigned. this allows multiple future
  search tree optimizations like handling of common dependencies
  early.

* merge common dependency names early to provide deeper forward
  checking.

also, discover late if package is needed or not.

Instead of "skipping" certain packages, we include them as-if required,
and at expansion time we decide if they actually need to be considered
for installation. This cleans up the expansion main loop a little bit
and makes the code work together better.

* cleaned up little bit on the internal state machine
* the decision applying mechanism now aborts early to avoid work
  if we are approaching bad solution candidate
* package availability checking is now done on-demand; which
  could still be improved