Adding issue15955_lzma_r5.diff. Main changes from r4:

* Consistent Py_ssize_t type for data_size
* max_size → max_length to match Python parameter name
* Arranged for EOF handling to occur before, and instead of, saving the input buffer
* Removed my LZMAFile test

Nikolaus, I hope I am not getting in your way by updating this patch. I though I should take responsibility for removing the test I accidentally added in r4.