Fix potential race condition in 'download_checkmd5.py'
Fix potential race condition in 'download_checkmd5.py'

scpeters/catkin,jack-oquin/catkin,ros/catkin,scpeters/catkin,asmodehn/catkin,ros/catkin,thaddeustaylor/catkin,wkentaro/catkin,wkentaro/catkin,harmishhk/catkin,jack-oquin/catkin,asmodehn/catkin,jack-oquin/catkin,harmishhk/catkin,asmodehn/catkin,scpeters/catkin,wkentaro/catkin,thaddeustaylor/catkin,thaddeustaylor/catkin,ros/catkin,harmishhk/catkin