hpx/util/safe_lexical_cast.hpp is added.
Some unprotected uses of boost::lexical_cast are wrapped by safe_lexical_cast.
Some default values has been added to safe_lexical_cast
Removed C++11 uniform initialization in default parameter of
safe_lexical_cast
Added get_entry_as function to avoid repeating parameters
Merge pull request #1270 from AntonBikineev/fixing_799

hpx/util/safe_lexical_cast.hpp is added.