Argument verification using partial matching

Simplification of function input argument checks. This concerns the following functions and arguments:

• CreateInputsCrit()
  • VarObs
• PE_Oudin()
  • LatUnit
  • TimeStepIn
  • TimeStepOut
• plot.OutputsModel()
  • which
• SeriesAggreg()
  • TimeFormat
  • NewTimeFormat

In the one-argument form match.arg(arg), the choices are obtained from a default setting for the formal argument arg of the function from which match.arg was called. (Since default argument matching will set arg to choices, this is allowed as an exception to the length one unless several.ok is TRUE rule, and returns the first element.)