NAME:daysinmonth
PURPOSE:give the nomber of days in a specefic month
CATEGORY: calandar
CALLING SEQUENCE: ndays = daysinmonth([month[, year]])
INPUTS (optionnal): month and year. Year is used only if the
common variable key_caltype = 'greg'. In that case, month
and year must have the same number of elements. if not
provided, we take month and year from "time" common variable.
KEYWORD PARAMETERS:
OUTPUTS:
COMMON BLOCKS: cm_4cal
SIDE EFFECTS: return -1 in case of error
RESTRICTIONS:
EXAMPLE: