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"' {} \;
```
Merge pull request #274 from chrisdembia/expandtabs-again

Convert tabs to spaces.