Comparing capy::error::canceled with std::errc::operation_canceled should pass

[anarthal]

The following fails:

std::error_code ec = boost::capy::error::canceled;
std::error_condition cond{std::errc::operation_canceled};
BOOST_TEST(ec == cond);

According to @pdimov, this should work. At the end of the day, capy::cond::canceled is equivalent to std::errc::operation_canceled. One possible option would be to remove capy::cond::canceled completely, and replace it by std::errc::operation_canceled. This would require overriding default_error_condition in the category, rather than equivalent.