xterm apparently supports ESC[90m through ESC[97m to set bright

xterm apparently supports ESC[90m through ESC[97m to set bright
foreground colours, and ESC[100m through ESC[107m to set bright
background colours. Hence, so do we. Bright-foreground is
distinguishable from bold, and bright-background distinguishable
from blink, when it leaves terminal.c; the front end may then choose
to display them in the same way if it's configured to do so. This
change makes the xterm backend for Turbo Vision (!!!) work properly.
Untested on Mac.

[originally from svn r2734]