[dune-pdelab] Issues with PDELab 2.4

[Christoph Grüninger]

Dear PDELab developers,
I just adjusted some Code of my from PDELab 2.0 to 2.4. I had 
these
issues:
- ImplicitEulerParameter no longer exists. I know I could use 
the theta
   scheme, but the ExplicitEulerParameter is still present. I 
assume it
   was forgotten in f778eaea677974eb57b14852e94a1cae8ee566c4
- The Doxygen comment for FractionalStepParameter is wrong, 
it's a
   copy-n-paste bug from the theta scheme.
- The consructors of GridOperator have the optional argument 
MatrixBackend
   which defauls to the default constructor. As MatrixBackends 
are no
   longer default constructable - BCRSMatrixBackend wants to 
get and integer
   estimate of its DoF per Element - this does not make much 
sense. I
   would prefer to get the error message, that I have to 
provide a
   MatrixBackend object.

If this are non-issues because the behavior is intended, I'm 
ok. If you
want to get patches, tell me. Hopefully this is not too late 
for
PDELab 2.4. I kind of lost track of the release schedule.

Bye
Christoph

-- 
Je n'ai rien contre les étrangers, quelques uns de mes 
meilleurs amis
sont des étrangers. Mais ces étrangers là ne sont pas de chez 
nous!
[Agecanonix, Astérix - Le cadeau de César]