math/sage security risk

[Stephen Montgomery-Smith]

After my recent conversations about creating a print/texlive-install 
port, I realize that my math/sage port might have a security risk.  This 
only happens if the user selects additional optional packages.  But the 
optional packages are downloaded post-fetch.

I'll make some immediate band-aid changes to the port to switch this 
off, but I'll think through the issue in the days to come.

Stephen