configure.ac: Use git-version-gen to set VERSION

We updated to 0.9.29 tag, but configure.ac was locked to 0.9.28, which
means release 0.9.29 is going to generated an old version and thus is
broken. A new release will follow this commit.

Change-Id: I8e1665f21d1bc76922423cabad3df72a2502f559
2 files changed