Fix some warnings caused by initialization lists being out of order
Make toolkits/graphical_models/utils.hpp non-executable
Fix graphlab not compiling with clang (Apple LLVM version 4.2)

Clang is a bit more strict than g++, and throws an error with this
code:

```
#include <vector>

template<typename T>
void add(T& t1, const T& t2) {
    t1 += t2;
}

template<typename T>
std::vector<T> operator+=(std::vector<T>& v1, const std::vector<T>& v2) {
    for (size_t i = 0; i < v2.size(); ++i) {
        v1.push_back(v2[i]);
    }
    return v1;
}

int main() {
    std::vector<int> v1;
    v1.push_back(5);
    std::vector<int> v2;
    v2.push_back(6);
    add(v1, v2);
}
```

The reasoning behind forbidding this code can be found here:

http://clang.llvm.org/compatibility.html#dep_lookup)

The fix in this case is pretty simple, it just requires moving
the `operator+=` in the distributed_graph_test test to before
the import of the graphlab headers.