patch 8.2.1967: the session file does not restore the alternate file

Problem:    The session file does not restore the alternate file.
Solution:   Add ":balt".  Works like ":badd" and also sets the buffer as the
            alternate file.  Use it in the session file. (closes #7269,
            closes #6714)
diff --git a/src/ex_cmdidxs.h b/src/ex_cmdidxs.h
index 2e59d2c..290e9fa 100644
--- a/src/ex_cmdidxs.h
+++ b/src/ex_cmdidxs.h
@@ -7,30 +7,30 @@
 {
   /* a */ 0,
   /* b */ 19,
-  /* c */ 42,
-  /* d */ 108,
-  /* e */ 133,
-  /* f */ 156,
-  /* g */ 173,
-  /* h */ 179,
-  /* i */ 188,
-  /* j */ 207,
-  /* k */ 209,
-  /* l */ 214,
-  /* m */ 276,
-  /* n */ 294,
-  /* o */ 314,
-  /* p */ 326,
-  /* q */ 365,
-  /* r */ 368,
-  /* s */ 388,
-  /* t */ 457,
-  /* u */ 502,
-  /* v */ 513,
-  /* w */ 533,
-  /* x */ 547,
-  /* y */ 557,
-  /* z */ 558
+  /* c */ 43,
+  /* d */ 109,
+  /* e */ 134,
+  /* f */ 157,
+  /* g */ 174,
+  /* h */ 180,
+  /* i */ 189,
+  /* j */ 208,
+  /* k */ 210,
+  /* l */ 215,
+  /* m */ 277,
+  /* n */ 295,
+  /* o */ 315,
+  /* p */ 327,
+  /* q */ 366,
+  /* r */ 369,
+  /* s */ 389,
+  /* t */ 458,
+  /* u */ 503,
+  /* v */ 514,
+  /* w */ 534,
+  /* x */ 548,
+  /* y */ 558,
+  /* z */ 559
 };
 
 /*
@@ -42,7 +42,7 @@
 static const unsigned char cmdidxs2[26][26] =
 { /*         a   b   c   d   e   f   g   h   i   j   k   l   m   n   o   p   q   r   s   t   u   v   w   x   y   z */
   /* a */ {  0,  1,  0,  0,  0,  0,  0,  0,  0,  0,  0,  4,  5,  6,  0,  0,  0,  7, 15,  0, 16,  0,  0,  0,  0,  0 },
-  /* b */ {  2,  0,  0,  4,  5,  7,  0,  0,  0,  0,  0,  8,  9, 10, 11, 12,  0, 13,  0,  0,  0,  0, 22,  0,  0,  0 },
+  /* b */ {  2,  0,  0,  5,  6,  8,  0,  0,  0,  0,  0,  9, 10, 11, 12, 13,  0, 14,  0,  0,  0,  0, 23,  0,  0,  0 },
   /* c */ {  3, 12, 16, 18, 20, 22, 25,  0,  0,  0,  0, 33, 37, 40, 46, 56, 58, 59, 60,  0, 62,  0, 65,  0,  0,  0 },
   /* d */ {  0,  0,  0,  0,  0,  0,  0,  0,  8, 18,  0, 19,  0,  0, 20,  0,  0, 22, 23,  0,  0,  0,  0,  0,  0,  0 },
   /* e */ {  1,  0,  2,  0,  0,  0,  0,  0,  0,  0,  0,  7,  9, 10,  0,  0,  0,  0,  0,  0,  0, 17,  0, 18,  0,  0 },
@@ -69,4 +69,4 @@
   /* z */ {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0 }
 };
 
-static const int command_count = 573;
+static const int command_count = 574;