Use configure for vala-bootstrap, not autogen.sh

vala-bootstrap's `autogen.sh` doesn't automatically run `configure`,
so the build breaks for lack of a `Makefile`. In addition,
vala-bootstrap already includes `configure`, so `autogen.sh` isn't
necessary.
Merge pull request #12 from ptomato/patch-3

Use configure for vala-bootstrap, not autogen.sh