Do not use VISUAL editor on dumb terminals
Refuse to use $VISUAL and fall back to $EDITOR if TERM is unset
or set to "dumb". Traditionally, VISUAL is set to a screen
editor and EDITOR to a line-based editor, which should be more
useful in that situation.
vim, for example, is happy to assume a terminal supports ANSI
sequences even if TERM is dumb (e.g., when running from a text
editor like Acme). git already refuses to fall back to vi on a
dumb terminal if GIT_EDITOR, core.editor, VISUAL, and EDITOR are
unset, but without this patch, that check is suppressed by
VISUAL=vi.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>