PATCH: Typo fixes, as found by doxygen.log

[Geert Janssens]

On Wednesday 3 March 2010, Jesse Weinstein wrote:
> The log of warnings from doxygen, doxygen.log, is actually quite useful.
> Here's a patch fixing various typos I found by looking through those
> warnings.  There are lots more to do...  Hopefully they should all be
> obvious once seen, but if not, I'll be glad to explain any of them in
> more detail.
> 
> Jesse Weinstein
> 

Applied in r18810. Thanks.

Geert