Update to Terminal Activity

[Phil Bordelon]

Michael Stone and I added a 'become root' button to the Terminal
tonight.  It is now part of Terminal-8.xo.

This consists of two parts:

* a new minimalist script, 'become_root', as part of olpc-utils;
* the button in Terminal.

The button is on the primary toolbar, with a new SVG created by
Michael and tweaked a bit by me.  All it does is paste
'become_root\n' at the terminal; the become_root script then
runs 'su -' or 'sudo' as appropriate.

This is meant to help mitigate a major upcoming support issue:
that of the flag-day switch between 'su -' and 'sudo' as the
primary method of running privileged commands.

We, of course, welcome any feedback on this additional feature.

Phil B.