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: