Actions:
* Remove superfluous includes to boost/date_time, iostream, and pragma_comp_defs.h
* Include cstdio for snprintf
* Include string for std::string
* Move get_gmt_time to top of module for following step
* Use thread-safe get_gmt_time instead of unsafe gm_time in function get_internet_time_str()
* In get_time_interval_string(), add explicit (int) casts to git rid of VS4996 warnings
* In get_time_interval_string(), use snprintf instead of boost::lexical_casts and string concats
* In file epee_utils.cpp, include boost/range/iterator_range.hpp for boost::make_iterator_range.
Previously, epee_util.cpp was including some file which was including time_helper which included
a boost header which included iterator_range.hpp at some point, which allowed epee_util.cpp to
compile without an explicit include of iterator_range.hpp. I added it because I removed the boost
includes in the first step which broke epee_util.cpp.
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