checking for last item in for loop

[Skaperen]

gotta run it forward. the loop does a series of compression.open calls using the open file object from the previous call as the "file" to be opened. each call must be binary except the last will be whatever was really needed. most times there is only one layer of compression. but sometimes there are more. the list being iterated is a list of compression modules to use for which algorithm that layer is going to use. a previous messy version works. this is to be a cleaner version that i will release under MIT license.