It allows tools which expect version in form major.minor to work
correctly even in case when pmdk is downloaded as zip archive.

This patch also removes '%d' from GIT_VERSION file. This placeholder
was filled with name of the branch only for the HEAD of a branch.
This means that GIT_VERSION of a selceted revision had different content
(either only commit hash or commit hash + name of the branch) depending
on whether selected revision was HEAD of the branch or not. Different
content of GIT_VERSION affected hash of the archive (and caused problems
with vcpkg in the past).