returns newest file of a set of files
k = newest(paths) k = newest(path1, path2, ..., pathn)
an integer: the index of the newest file.
a character string vector, paths(i) is the pathname of i-th file.
a character string, the pathname of i-th file
Given a set of pathnames newest returns the index of the newest
one. Non existent files are supposed to be the oldest.