pkg-create.8: Update @dir-related documentation to match latest Porter's Handbook
Fix unit test
pkg-version: New configuration option VERSION_SOURCE

This allows to set the default database used for version number
comparison.

Conflicts:
	docs/pkg-version.8
	docs/pkg.conf.5
	libpkg/pkg_config.c
pkg_add: do not emit error on installed packages
Fix bad merging