Add in PREFIX/etc/julia/juliarc.jl file for site-specific commands

Lays the groundwork for addressing #4222 

This should replace the mess of environment variables being set in the OSX binary distribution so that we can simply invoke the executables directly and get the environment we need.  Additionally, this `juliarc.jl` file is included _before_ the user's personal `juliarc.jl` file so that if the user desires, they can override settings, etc...

@vtjnash @stevengj