[Developers] remove dependency of NaNChecker from MoL

[Thomas Radke]

Erik Schnetter wrote:
> Many people use MoL without the NaNChecker; if MoL requires the  
> function, NaNChecker always needs to be present, even if it is not  
> used.  That is inconvenient.  I would keep it as "uses" and add a run- 
> time check depending on MoL's parameter settings.

If I remember right a thorn needs to be activated in order to provide 
aliased functions. Yes, then this would be inconvenient.

>> There is no convention about names for aliased functions but I suggest
>> to prefix them with the name of the providing thorn/implementation.
> 
> 
> That would require renaming the existing function, which we shouldn't  
> do.  Do you have a suggestion for a good name?

Not really, and I don't know how many thorns would need to be changed to 
use renamed functions. So maybe we should just stick with 
CheckVarsForNaN() and SetVarsToNaN().

-- 
Cheers, Thomas.