RcppArmadillo 0.4.550.2 with Armadillo 4.550.2

contains fix for g++-4.4.*, with special thanks to Conrad
should address #30 and #31 reported earlier today
Merge pull request #32 from RcppCore/feature/arma-4.550.2

RcppArmadillo 0.4.550.2 with Armadillo 4.550.2