Ambiguous arithmetic operators for NumericVector op int on 32 bit

[dcdillon]

The arithmetic operators involving both NumericVector and NumericMatrix and int were causing R CMD check failures on 32 bit. Actually, the same error can be exposed on 64 bit by replacing int with long (specifically the integral type that is the same size as a pointer on the given architecture).

I have come up with a fix for this and will PR in a few minutes. This will need some extra eyes (@eddelbuettel, @thirdwing I'm looking at you) and probably a revdep check.

[eddelbuettel]

Done in #476