Made hadoop_jar fix_paths able to handle trailing slashes

I began using luigi and got caught out by the fact that fix_paths in hadoop_jar.py assumes that directories given for a hadoop job as arguments do not contain trailing slashes. If you give a trailing slash then the eventual move from the "temp" directory to the real one will give an error, as you are moving from /a/b/c/luigi-tmp-19i403/ to /a/b/c/ (what we wanted was to use /a/b/c-luigi-tmp-19i403/ as a temporary directory instead).

I added a line which should sort this out, I'm assuming that other people use trailing slashes and it is not a weird thing that only I do. I may be wrong there.