COMP: Fix download of pydicom using valid URL

This commit re-enables download of pydicom. It started to fail either because
the package has been explicitly removed from googlecode or because google
is shutting down the system as explained in [1]. Either way, download should
now be fixed.

[1] https://google-opensource.blogspot.com/2015/03/farewell-to-google-code.html

git-svn-id: http://svn.slicer.org/Slicer4/trunk@25314 3bd1e089-480b-0410-8dfb-8563597acbee