build-sys: bump also PACKAGE_VERSION_RELEASE number

build-sys: bump also PACKAGE_VERSION_RELEASE number

Now we bump only PACKAGE_VERSION_MAJOR and PACKAGE_VERSION_MINOR
numbers. The PACKAGE_VERSION_RELEASE is always zero.

These numbers are used for LIBxxx_VERSION strings and Version: field
in the .pc files.

Unfortunately, if we keep PACKAGE_VERSION_RELEASE= always zero then
our bugfix releases are invisible for pkg-config.

(Although I don't think it's good idea to depend in code on any
 library bugfix release, code should be about APIs).

Addresses: https://github.com/systemd/systemd/pull/1754
Signed-off-by: Karel Zak <kzak@redhat.com>