Updated TerrainProfileGraph and AnnotationEvents

Glenn -

I've fixed a couple of the bugs that I identified earlier. Please let me know if these can be incorporated into the main code line. This is obviously my first commit to osgEarth, so please let me know if there's a protocol you'd like to observe and/or if there's anything I should be doing differently.

Also, I'm new to git, so I'm not certain if you can see my commit messages, which explain each of the changes. If not, let me know and I'll post them too.

Michael