Don't "make vapi" unless building from git checkout: Closes bgo#723704

There's really no need for a tarball build to generate the VAPI file,
so that capability's been removed.  "make vapi" will only work from
within a repo checkout.
configure.ac cleanup

Mailing list address and project URL updated to GNOME.  Don't generate
.gz tarball, only .xz.
Fix --enable-introspection: Closes bgo#723705

Not only fixes the configure switch, but fixes the g-ir-scanner step
itself and updates the namespace version.
gexiv2 0.9.1