patch 8.2.0590: no 'backspace' value allows ignoring the insertion point

Problem:    No 'backspace' value allows ignoring the insertion point.
Solution:   Add the "nostop" and 3 values. (Christian Brabandt, closes #5940)
diff --git a/src/option.c b/src/option.c
index fa4d188..504ddf4 100644
--- a/src/option.c
+++ b/src/option.c
@@ -1685,6 +1685,10 @@
 					*(char_u **)varp = vim_strsave(
 						(char_u *)"indent,eol,start");
 					break;
+				    case 3:
+					*(char_u **)varp = vim_strsave(
+						(char_u *)"indent,eol,nostop");
+					break;
 				}
 				vim_free(oldval);
 				if (origval == oldval)
@@ -6818,7 +6822,7 @@
  */
     int
 can_bs(
-    int		what)	    // BS_INDENT, BS_EOL or BS_START
+    int		what)	    // BS_INDENT, BS_EOL, BS_START or BS_NOSTOP
 {
 #ifdef FEAT_JOB_CHANNEL
     if (what == BS_START && bt_prompt(curbuf))
@@ -6826,7 +6830,8 @@
 #endif
     switch (*p_bs)
     {
-	case '2':	return TRUE;
+	case '3':       return TRUE;
+	case '2':	return (what != BS_NOSTOP);
 	case '1':	return (what != BS_START);
 	case '0':	return FALSE;
     }