get_version: always include the release number, even if it's 0

Previously, the verion number would be "a.b.c" unless c==0, in which
case it would be "a.b".

Now the version number scheme is always "a.b.c", even if c==0.

(cherry picked from commit 330a4aaf30780daeb7621cfeba76b1438b6bf4e9)
make config/hwloc_get_version.sh executable

(cherry picked from commit 08a664cbcd3846499de7096bd6b5ee20303dc192)