builder: allow to build different versions of one package
builder: allow to build different versions of one package

When we start using timestamps in snapshots of directories,
we can build different versions of one package in one session
without any harm.

Also it will fix the problem when installer installs old existent version
of package and the builder trying to build new version
and throws an error:
"Asked to build perl/Scalar-List-Utils=1.47:1 when
perl/Scalar-List-Utils=1.46 already built"

xsawyerx/pkt,xsawyerx/pakket,xsawyerx/pakket