Test and update DCMTK version to benefit from performance enhancements

[fedorov]

Following on email from @michaelonken:

I recently looked into the performance issue with writing segmentations
(and other objects based on functional groups).

As I thought, the main speed issue is the checking of the functional
group structure. It's possible to speed this up (I think) by changing
the way functional groups are organized and accessed in memory and I put
it on my list to enhance this in the future.

For now, I did two things:

• For some objects the checking has been performed twice, including
  segmentations, i.e. updating to new code will speed up writing by
  factor ~2.

• Also, if you use the same code over and over again to produce the
  segmentation objects, you probably do not require to check the
  correctness of the functional groups at all. In such cases it only makes
  sense to use the checking when you develop your own code and test with
  some instances.

As an impliciation I think it is useful to just optionally disable the
checks. That's now possible too and makes writing even large
segmentation objects very fast.

You could test this with the latest DCMTK, e.g. commit
9461c7851c3465ca0f14b964ed7c6d0dd4d88834 (latest online right now).

The actual commit with the check option is this one:
591a1bc2f0ad0edec4fbb093ceb07b5fcaf127c9 .

You can disable checks by setting setCheckFGOnWrite(OFTrue) on your
DcmSegmentation object.

[fedorov]

@michaelonken can you give us some unofficial idea if a minor release is coming up sometime soon?

[michaelonken]

It's planned for late summer...this year :-).

[fedorov]

Resolved by #391

[fedorov]

TODO: need to test with checks disabled ...