Fix compatiblity with G++ 4.7

Hi,

I had some problems to build your project on a Debian Wheezy with G++ 4.7.
Here is the patch that solved my build issues.

The option ``-std=c++0x`` refers to the experimental support of the C++11 draft.
But C++11 isn't a draft anymore, and the correct option is now ``-std=c++11``.

By the way, the exception ``std::runtime_error`` is defined in the header ``stdexcept``, it needs to be included.

Cordially,
David Delassus.