git-shortlog man page missing a bunch of options

Hi,

I was looking at the git-shortlog man page today and realized that it didn't mention an option that I have used before '--no-merges'. Looking further, there are a lot of options that are not documented.

One fix would be to include rev-list-options.txt (which is where I assume these options come from), just like git-log does.

But rev-list-options.txt is a rather large file and I'm not sure if including it in both git-log and git-shortlog would be a good idea. The way I see it, git-log is the "primary" log interface, and git-shortlog is a "secondary" log interface, so git-log warrants such a large man page, but git-shortlog doesn't especially since most options are repeated. So maybe it is a better idea to just include a pointer to git-rev-list in the shortlog man page.

I'll send in a patch after some suggestions on which alternative to go for.