Remove std::isnan and std::isinf usage from utFastAtofTest

These functions were added in C++11, and should not be used nakedly
in the current code base. Replace them with suitable C++03 constructs.
Merge pull request #376 from jdduke/make_fast_atof_test_cpp03

Remove std::isnan and std::isinf usage from utFastAtof test
Merge remote-tracking branch 'upstream/master'