Doxy fixes

My doxygen build doesn't create the same errors that @gonuke was reporting in #506 (probably just a different version of Doxygen). I don't get the Material class error, the KahahSum one, or the BuildingManager one (this latter one is not from my pr, btw).

This is all that Doxygen gives me: 
```
Searching for member function documentation...
/Users/khuff/repos/cyclus/src/Core/Utility/CycArithmetic.cpp:35: warning: no matching class member found for 
  vector< double > CycArithmetic::sort_ascending(vector< double > to_sort)
Possible candidates:
  static std::vector< double > CycArithmetic::sort_ascending(std::vector< double > to_sort)
  static std::vector< double > CycArithmetic::sort_ascending(std::map< int, double > to_sort)

/Users/khuff/repos/cyclus/src/Core/Utility/CycArithmetic.cpp:41: warning: no matching class member found for 
  vector< double > CycArithmetic::sort_ascending(map< int, double > to_sort)
Possible candidates:
  static std::vector< double > CycArithmetic::sort_ascending(std::vector< double > to_sort)
  static std::vector< double > CycArithmetic::sort_ascending(std::map< int, double > to_sort)

```

So, this PR fixes those two and applied the same solution to the KahanSum one and the Material::applyThreshold function in the hopes that it would fix those for you too (can you check, @gonuke?).  However, I have no idea what to do about the BuildingManager one, because it has way too many layers of namespaces for me to feel comfortable fooling with it. @gidden will have to fix that one.

Anyway, the errors above don't make any sense, because it seems as though doxygen is just failing to recognize the "using namespace std" directive. . . which... I thought wasn't a problem anywhere else in the code. That said, this issue would indicate that this is the case http://stackoverflow.com/questions/15063270/having-doxygen-aware-of-namespace-in-cpp .