Bugfix for dx download -r when given a relative path
(cherry picked from commit 1c5f22613247495815e5339d9ba6c2e9447c6061)

Conflicts:

	src/python/test/test_dxclient.py
Further bugfix for dx download -r for relative paths with trailing slash
(cherry picked from commit 3a10d410c1eaaf6d6b826eb0431cc89975dd2192)