Qualify begin() and end() in the C++98 code

[mfeemster]

If prettyprint98.hpp is being built with a C++11 compiler, the calls to begin() and end() are ambiguous with the std:: versions of them, and produce an error. Qualify them like so around line 197:

if (pretty_print::begin(_container) != pretty_print::end(_container))
            for (TIter it = pretty_print::begin(_container), it_end = pretty_print::end(_container);;)

I'm sure the intent with the C++98 version is that it is *not being built with a C++11 compiler, but just to be safe.