Revert "Remove caTools dependency"

This reverts commit e4239c924b87f55859d5fd7541b5169462f7c1df.

I totally forgot the problems this causes with R 2.15 and thus
glimmer/spark. httpuv 1.2.2 requires Rcpp 0.11 which requires
R 3.0. So existing installs (like glimmer/spark) that are
running just fine with httpuv 1.2.0 will be forced to upgrade,
which is hard to do when you don't know the provenance of
all the packages installed by your users.