error message when compiling with clang++ in C++11 mode 

In C++11 mode, clang++ gives the following error at several lines in spec_retriever.cpp

error: non-constant-expression cannot be narrowed from type 'size_t' (aka 'unsigned long') to 'int' in initializer list [-Wc++11-narrowing] 

We can override this message by inserting an explicit cast.