minor improvements to STIR Hessian code (require STIR 6.3)

[KrisThielemans]

• call accumulate_Hessian_times_input in the no-subset case, as this will now be a bit faster (it's also a tiny bit less code)
• give correct name of parameters in cstir.h to avoid confusion
• add test for objective function with prior
• clarify RDP exclusion of test case

[KrisThielemans]

test_Hessian is currently failing here:

>       assert q <= .002
E       assert 8.509224046411635 <= 0.002

src/xSTIR/pSTIR/tests/test_ObjectiveFunction.py:83: AssertionError
----------------------------- Captured stdout call -----------------------------
norm of (x): 723.340454
norm of (x + dx): 724.102478
norm of grad(x): 12292.545898
norm of grad(x + dx): 12304.041016
norm of grad(x + dx) - grad(x): 11.830816
norm of H(x)*dx: 103.441887
relative difference: 8.509224

I believe this is because the STIR fix still needs to be fixed (as with that fix, my local test works ok). This would be a good thing: a test that fails because there's a bug!

We will need to update our STIR version requirements therefore. Obviously, with STIR 6.2, all Hessian tests will/should fail.

I think the easiest thing will be to require STIR 6.3. If people complain, we can always put in some code to allow 6.2, but throw explicit errors when the Hessian code is called (due to #1343 or UCL/STIR#1648)

[KrisThielemans]

Depends on #1347

[KrisThielemans]

I've rebased this on master, after the previous large merge. I've also updated to require STIR 6.3.

I now expect the DEVEL_BUILD=OFF job to fail, but ON to succeed.

[KrisThielemans]

I now expect the DEVEL_BUILD=OFF job to fail, but ON to succeed.

indeed

[KrisThielemans]

@evgueni-ovtchinnikov @paskino please update the SIRF-SuperBuild to use DEFAULT_STIR_TAG to current STIR master

[KrisThielemans]

SIRF-SuperBuild updated, so the non-devel BUILD should now work.

[KrisThielemans]

CI is now re-running