th a header.
eb:	Edit then use both versions.
el or e1:	Edit then use the left version.
er or e2:	Edit then use the right version.
e:	Discard both versions then edit a new one.
l or 1:	Use the left version.
r or 2:	Use the right version.
s:	Silently include common lines.
v:	Verbosely include common lines.
q:	Quit.
