Fixes #67960 - Long/short day names reversed in jddayofweek()

See https://bugs.php.net/bug.php?id=67960

We reverse the definitions of the constants, so that `CAL_DOW_LONG` is now `1` and `CAL_DOW_SHORT` is now `2` so that they correspond with the definitions given in the documentation at http://www.php.net/function.jddayofweek

This means we need to reverse their usage in the code.  Note here that previously, `CAL_DOW_LONG` selected the short names `daynames` and `CAL_DOW_SHORT` selected the long names `daynamel`!

The test script is now driven from the constants - and since we test their numeric values in the expected output, we are checking that they are set consistently.