Convert tabs to spaces.

Done with:
```
find . -name 'CMakeLists.txt' -or -name '*.cpp' -or -name '*.c' -or -name '*.h' ! -type d -exec bash -c 'expand --tabs 4 "$0" > /tmp/e && mv /tmp/e "$0"' {} \;
```

@sherm1, quick! Here's our chance!

For any future PR's or branches that would suffer as a result of this change, I will resolve your conflict for you. Just @mention me in your PR and ask me to add a commit that converts tabs to spaces, and will thus get rid of the conflict.

After this gets in, I will modify the travis test to fail if there are any tabs.

View this PR with ?w=1 in the URL.