minor updates to cell-centered exact projection implementation
minor updates to cell-centered exact projection implementation

huahbo/IBAMR,huahbo/IBAMR,iamciera/IBAMR,iamciera/IBAMR,yaojieuh/IBAMR,iamciera/IBAMR,yaojieuh/IBAMR,yaojieuh/IBAMR,huahbo/IBAMR,huahbo/IBAMR,huahbo/IBAMR,iamciera/IBAMR,yaojieuh/IBAMR,yaojieuh/IBAMR,iamciera/IBAMR,huahbo/IBAMR,iamciera/IBAMR,huahbo/IBAMR,yaojieuh/IBAMR,yaojieuh/IBAMR,iamciera/IBAMR