Revert r299218 VISUAL is actually a perfecly valid env to specify an editor

usr.bin/sdiff/edit.c

@@ -40,7 +40,10 @@ editit(const char *pathname)
 	int saved_errno, st, ret = -1;
 	const char *ed;
 
-	if ((ed = getenv("EDITOR")) == NULL)
+	ed = getenv("VISUAL");
+	if (ed == NULL)
+		ed = getenv("EDITOR");
+	if (ed == NULL)
 		ed = _PATH_VI;
 
 	sighup = signal(SIGHUP, SIG_IGN);

usr.bin/sdiff/sdiff.1

@@ -4,7 +4,7 @@
 .\" Written by Raymond Lai <ray@cyth.net>.
 .\" Public domain.
 .\"
-.Dd May 7, 2016
+.Dd $Mdocdate: July 5 2012 $
 .Dt SDIFF 1
 .Os
 .Sh NAME
@@ -50,6 +50,8 @@ into
 In this mode, the user is prompted for each set of differences.
 See
 .Ev EDITOR
+and
+.Ev VISUAL ,
 below,
 for details of which editor, if any, is invoked.
 .Pp
@@ -131,10 +133,22 @@ Change the size of tabs (default is 8.)
 .El
 .Sh ENVIRONMENT
 .Bl -tag -width Ds
-.It Ev EDITOR
+.It Ev EDITOR , VISUAL
 Specifies an editor to use with the
 .Fl o
 option.
+If both
+.Ev EDITOR
+and
+.Ev VISUAL
+are set,
+.Ev VISUAL
+takes precedence.
+If neither
+.Ev EDITOR
+nor
+.Ev VISUAL
+are set,
 the default is
 .Xr vi 1 .
 .It Ev TMPDIR