Fixes #24.

Calculate changesets directly by stabilizating the package graph instead of
recalculating the whole graph and then diffing (similar approach as seen
in 'smart' package manager). The algorithm is not complete: defferred
search space forking is missing. So you don't always get a solution on
complex graphs.

Benefits:
- usually the search state tree is smaller (less memory used)
- speed relational to changeset size, not database size (usually faster)
- touch only packages related to users request (can work on partitially
  broken state; upgrades only necessary packages, fixes #7)

Also implemented:
- command prompt to confirm operation if packages are deleted or downgraded
- requesting deletion of package suggests removal of all packages depending
  on the package being removed (you'll get list of packages that also get
  removed if you want package X removed)
- option --simulate to see what would have been done (mainly for testing)
- an untested implementation of versioned dependencies and conflicts

A lot has changed, so expect new bugs too.

This will be used later by the commit change calculator (for improved
changeset calculation, ref #7). Will be also used by "apk info" to show
reverse dependencies or "required by" information.

So we don't get artificial limits on the amount of dependencies
(fixes #8).

So you will not get .apk-new files of the new configuration files.

we let bb use /bin and /sbin, all packages overriding busybox must
install the bins in /usr/bin and /usr/sbin

apk_hash_delete() actually deletes the file entry, so unlinking
from other lists need to happen before that. Also free the diri
instead of leaking it.

We dont care if a directory have references or not, we care if directory
is relly there.

Only the creator of the direcotry will set the permissions.

This fixes the situation where you install a package owning a dir then
you remove this dir manually and try install a second package also owning
the dir.

For example:

  apk add e2fsprogs-dev
  rm -rf /usr/lib/pkgconfig
  apk add zlib-dev

Otherwise creating rootfs from scratch with --initdb cannot be locked
due to the lock file path missing.

Protect files in protected dirs even if the file is not previously
registered in the database. We do so by always extracting to a
.apk-new file name, compare the checksums afterwards and rename if
file was identical.

Add flags field to db open call. Also make error reporting quite a bit
more detailed.

Otherwise installed db load fails due to internal reasons. This would
cause a lot of other funny stuff happen.

Ignore /etc/apk/repositories, so additional repositories that depend
on other repositories need to have explicit --repository reference on
command line when generating the index (to avoid warnings).

This was broke on --initdb addition to add applet since apk_db_create
changes the working directory.

this allows non-root users to query the database.

But we dont bother try create all subdirs (i.e mkdir -p ...)

Currently only implement --backup to get list of (config) files in
protected directories to backup.

This also fixes a database corruption bug in database.c.

In quiet mode e.g. "apk info -q -W <file list>" a list of dependencies
suitable for .PKGINFO is output in one line.

dependencies are separated with single space rather than ', '.
makes db file slightly easier to parse from a shell script which
might be handy.

Defaults to /etc/apk/repositories, absolute path and not relative
the install root.