better exception handling

[piccolbo]

instead of catching all exceptions in C++, use the technique explained tersely here http://cran.r-project.org/web/packages/Rcpp/vignettes/Rcpp-introduction.pdf section 7.1. This has to goal of returning the exception to the R level where it can be handled better and also eliminating warnings about using stderr from C, which happens only with exceptions, which is reported to be less portable.

[piccolbo]

I tried and it segfaults like there's no tomorrow. Not worth the effort