add a two digit increment to a filename
local df = require "lib/dtutils.file" local result = df.filename_increment(filepath)
filepath - string - filename to increment
filename_increment solves the problem of filename conflict by adding an increment to the filename. If the supplied filename has no increment then “01” is added to the basename. If the filename already has an increment, then 1 is added to it and the filename returned.
result - string - the incremented filename
The filename will be incremented to a maximum of 99.