[R] install.packages() for a local file

[Jeff Gentry]

> There is a method to install a package from a local file.
>  From the unix command line, use
>    R INSTALL
> possibly using
>    R CMD build
> first.

Right.  

I already do this within the function (I need to install the packages from
inside of R), but was going through trying to find redundant code and
thought this might be a place where I could replace one of my functions
with a call to one of R's functions.