Noticed a few typos while reading through the docs.

Not sure how to report this so I'm making a bug report. I've attached a patch generated with git-format-patch(1). Hope that's alright.

One of the typos shows up in a few places. Can be seen with:

$ grep -ir "\ a\ a\ "

I haven't done anything to the occurrences of that typo in old "ChangeLog" files; didn't want to upset anything.