patch 9.1.0218: Unnecessary multiplications in backspace code

Problem:  Unnecessary multiplications in backspace code, as
          "col / ts * ts" is the same as "col - col % ts".
Solution: Change "col / ts * ts" to "col - col % ts".  Adjust the loop
          and the comments ins_bs() to be easier to understand.  Update
          tests to reset 'smarttab' properly.
          (zeertzjq)

closes: #14308

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/version.c b/src/version.c
index 3067d75..4523359 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,10 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    218,
+/**/
+    217,
+/**/
     216,
 /**/
     215,