[plug] [OT] Perl feature detection

[James Devenish]

Hi,

Does anyone know the conventional way that one can determine whether
Perl is running with support for the three-argument (3-argument) form of
the 'open' function? I don't know what version of Perl first supported
the three-argument function. The reason, and perhaps the way I should
have phrased my question, is "what is the correct way to fall back to a
two-argument form if the three-argument form is not available?"