The installer now respects RBINSTALL_COLOR and RBINSTALL_INTERACTIVE

environment variables. The former allows for the equivalent of

--no-color (when set to 0), and the latter `--noinput (when set

to 0).
The bootstrapper now provides some safety instructions immediately

before handling control off to the main installer. These tell the user

that if they can't see or run the installer, set RBINSTALL_COLOR=0 and

try again, or contact support.
This is intended as an aid for anyone who may have trouble seeing the

installer. One user encountered this in a tmux environment running on

Ubuntu Linux in, presumably, GNOME Terminal. While we haven't been able

to reproduce the cause, the hope is that this will prevent people from

getting completely stuck.

Ran the installer and saw the new bootstrap text changes.
Verified that the new options controlled the behavior of the installer.