Pg simple update

[paul-vdb]

Three changes:

1. Initiate inflationNodes to avoid a small error when check = FALSE.
2. Ensure initializeX=FALSE if a design matrix is passed
3. Add a warning if infinite values are found in the design matrix. Suggests to scale the design matrix in advance.

@paciorek Should we put a full stop if infinite values are detected in the design matrix instead of a warning?
Does it make sense to allow the user to override this warning? Currently infiniteOkay is a list input. Better name? I need to add it documentation still.

[paciorek]

Sorry about the delay in looking at this. I have some questions.

1. Regarding the user providing inflationNodes if checking is not being done, I don't see why we need to have the user provide. Checking is just to make sure things are all valid and if the user doesn't want that done, I think we just find the inflationNodes using getParents and setDiff(inflationNodes, nonTarget). I.e., move those lines of code that initially determine inflationNodes outside of if(check). Am I missing something?
2. Could we actually have valid computation in the sampling if there are Infs in X? I think we would get an invalid sample. So unless I'm missing something I think we should error out and not provide an override.

[paul-vdb]

@paciorek Thanks. I'll make the suggested changes this afternoon and merge into devel if there are no conflicts etc.