configure.ac: post-release version bump to 3.17.2
configure.ac: post-release version bump to 3.17.2

sfeltman/pygobject,GNOME/pygobject,GNOME/pygobject,sfeltman/pygobject,sfeltman/pygobject,pexip/pygobject,pexip/pygobject,pexip/pygobject,GNOME/pygobject