if MAIL_CHECK_ENAB is disabled, then don't export the MAIL envvar

--- libmisc/setupenv.c
+++ libmisc/setupenv.c
@@ -265,16 +265,18 @@
 	 * knows the prefix.
 	 */
 
-	if ((cp = getdef_str ("MAIL_DIR")))
-		addenv_path ("MAIL", cp, info->pw_name);
-	else if ((cp = getdef_str ("MAIL_FILE")))
-		addenv_path ("MAIL", info->pw_dir, cp);
-	else {
+	if (getdef_bool ("MAIL_CHECK_ENAB")) {
+		if ((cp = getdef_str ("MAIL_DIR")))
+			addenv_path ("MAIL", cp, info->pw_name);
+		else if ((cp = getdef_str ("MAIL_FILE")))
+			addenv_path ("MAIL", info->pw_dir, cp);
+		else {
 #if defined(MAIL_SPOOL_FILE)
-		addenv_path ("MAIL", info->pw_dir, MAIL_SPOOL_FILE);
+			addenv_path ("MAIL", info->pw_dir, MAIL_SPOOL_FILE);
 #elif defined(MAIL_SPOOL_DIR)
-		addenv_path ("MAIL", MAIL_SPOOL_DIR, info->pw_name);
+			addenv_path ("MAIL", MAIL_SPOOL_DIR, info->pw_name);
 #endif
+		}
 	}
 
 	/*