ENH: Add REQUIRES_DISPLAY CTest label.

This is added to tests, like the VtkGlue tests, that require a working DISPLAY
to render their output.  They are labeled so they can easily be excluded by
dashboard builds that run on a headless server.

Change-Id: I029facdfec924d23b54815825b53ae3ebd0784cd
COMP: Bump DCMTK to fix warning.

The previous CMake related patch not integrated upstream was rebased on the
upstream DCMTK-3.6.1_20131114 tag, d60870a5b9bbb9792f63d9c929358446f50f1b88.
Upstream has fixed a warning in CMake/3rdparty.cmake:9:70:

CMake Warning (dev) at CMake/dcmtkPrepare.cmake:288 (INCLUDE):
Syntax Warning in cmake code at

   CMake/3rdparty.cmake:9:70

Argument not separated from preceding token by whitespace.

Co-authored by Brian Helba <brian.helba@kitware.com>

Change-Id: Ie21356974bbf58c9bac5421789bfbdee7427be80
Merge topic 'dcmtk-bump'

50101e6b COMP: Bump DCMTK to fix warning.
Merge topic 'display-label'

62ee946d ENH: Add REQUIRES_DISPLAY CTest label.