Address deprecation of Matrix command

[smeisler]

Address deprecation of Matrix command (see warning below)

SETTING UP DATA 
 MAKING DESIGN MATRICES 
 RUNNING MODELS 

 .. LEFT CORTEX ANALYSIS 
     848 locations removed due to NA or NaN values.
     86 additional locations removed due to low mean.
.... prewhitening... done!

.... estimating model with EM... FINDING BEST GUESS INITIAL VALUES
as(<ddiMatrix>, "dgCMatrix") is deprecated since Matrix 1.5-0; do as(as(., "generalMatrix"), "CsparseMatrix") instead

[damondpham]

Thanks!! I moved your change to a new development branch, 4.0. You can start using this branch and we'll make changes here as needed!