(split) COMP: Update FLTK SVN configuration.

Upstream FLTK changed their SVN server configuration.  The domain name
has changed and a checkout now requires a blank username and password.

Since the currently released version of CMake does not support an empty
username and password in the SVN checkout, a custom DOWNLOAD_COMMAND
is used for the FLTK ExternalProject.

Change-Id: I9f59b84d585bfcb69ad063534e6f21be8f8f165a
(split) ENH: Bump VTK ExternalProject to 5.10.1.

Change-Id: I13ae6552c597546cd4262171ec683ae582478e8c
Merge branch 'Superbuild-latest' of /home/matt/progs/ITKApps
Merge commit '6c7faa438dcca5d6973e5836dd11831a105491d0'

Conflicts:
	Superbuild/External-VTK.cmake