Make the libapk and lua module optional at buildtime and off by default.
This is because enabling libapk requires that mkinitfs also copies the
libapk.so or the initramfs will not work.

To build libapk:

 make LIBAPK=yes

To build lua module (will enable LIBAPK=yes):

 make LUAAPK

To link apk to libapk (will enable LIBAPK=yes):

 make SHARED_LIBAPK=yes

All the above applies to make install target as well.

So open the db in read-only mode instead. This allows --simulate to
be run as non-root user.

Take the uid/gid from passwd and group.

The triggers are read during apk_db_unpack_pkg(). If we delete the
triggers list after then unpack we delete the triggers which is not
what we want.

This fixes bug introduced in ce3cf8bf

got broken to the previous array cleanup and grepping struct
definition only from headers.

Instead of having a null pointer, use a dummy array which just
says the array is empty. This helps in multiple places of the code
which would otherwise need explicitly need to check first if the
array exists. This has been cause of multiple seg.faults in the
past as the array check is easily omitted.

This also removes (or fixes) all existing checks accordingly.

clean up the triggers properly, in proper order.

especially important if the package requested from command line
does not exist. otherwise we would not print an error at all.

Print more information why installation changeset calculation failed.
Fixes #187.

To print upgrading if package is actually being changed instead of
pure reinstall.

If version is equal, but package contents are different we should
show the package being upgraded.

In addition to autocleaning dependencies on deletion, we need to
autoclean the old package on upgrade too. This is to make sure that
obsoleted dependencies (existed previously, but not in new package)
are removed where appropriate.

openssl BIO does not close the fd unless we explicitly tell it to
do so.

So it'll be easier to rebuild affected packages. Fixes #349.

Doing "apk add file.apk" adds a versioned dependency to allow
downgrading, and sticky version. Most often this is to install
single packages from newer repository. So it would make sense
to reset them to non-versioned if doing:

 apk upgrade -a

fixes #346

Check that package name has packages associated with it before
dereferencing the pointer. Fixes #345.

they do not have any package associated. this is indicated by
package with zero installed_size.

even if we have only one package as candidate, we need to check
it's availability. otherwise we can endup with bad changeset
referring to unavailable package.

we do not create mirror repositories from other valid repositories,
not from what was installed locally.

wget:ing local files results in error and is useless.

add the missing variable.

otherwise regeneration of non-repository index might go wrong or we
might delete too many files from cache when doing 'cache clean'.

prints like:
(1/12) Installing...
(2/12) Installing...
etc...

This makes things a little bit nicer when installing from network with
slow lines.

We want see all packages that fails to install and not only the first

got broke few commits ago when apk_pkg_installed() call was
moved to happen after the package name has been read.

When pressing only <enter> on the question "..continue [Y/n]?" then
lets take that as a "yes"