In Emacs, `M-x shell` creates a shell buffer with very rudimentary
terminal capabilities. `$TERM` is set to `dumb`, and `echotc Co`
fails after printing `echotc: no such capability: Co` to standard
error. If our goal was to determine whether the terminal supports 256
colors, we really have no information to go on. I recommend that we
trust the user and hope for the best. That means we should (1)
discard any `echotc Co` error output, and (2) forego the warning
message about having fewer than 256 colors if `echotc Co` failed.
