fix reduce counter issue
ignore additional mr support files
make unique names when writing side files concurrently, then pick any nonempty one
rely on hadoop to know which file we are reading
do not use fname as directory if there aren't any sections
backend independent du
pick one of equivalent sections
reuse rmr.normalize.path
recursive mkdir
section selection factored out to get.section and responsbility goes to make.keyval.reader
make.keyval.reader now only needs a directory to work with, takes care of the rest