Large commits to asf-site do not trigger site rebuild

Several times now, I have done large commits to asf-site branch, pushed them, and gitsubpub did not get triggered. I have to do a follow-on trivial commit, and then it is triggered. This is a bit of a problem, because we have some auto-generated content that will always have a few lines different. These add up to a big commit.

I can tell when it is not going to work when my commit doesn't show up in #asfbot IRC channel.