Regression on process_cpu_clock::timepoint io on V2

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The following example

#define BOOST_CHRONO_PROVIDES_DEPRECATED_IO_SINCE_V2_0_0
#include <boost/chrono/chrono_io.hpp>

int main() {
  std::cout<< boost::chrono::process_cpu_clock::now() << std::endl; 
}

outputs

{1383629724660000000;0;0} nanoseconds since process start-up

while if BOOST_CHRONO_PROVIDES_DEPRECATED_IO_SINCE_V2_0_0 is not defined, it outputs

1383629672240000000 nanoseconds since process start-up

A process_cpu_clock::duration::rep is a tuple like of 3 clocks real, user and system.

The same problem for input. V1 manages a format {v1,v2;v3} and is able to restore the 3 clocks, but V2 takes only the real clock in account.

[viboes]

​https://github.com/boostorg/chrono/commit/a60274c77ab8b53fdd77fbc109fc9d344824d6d5

[viboes]

Merged to master ​https://github.com/boostorg/chrono/commit/143260daeb2703961448a0928d199747ca34dfca