patch 8.0.0514: script for creating cmdidxs can be improved

Problem:    Script for creating cmdidxs can be improved.
Solution:   Count skipped lines instead of collecting the lines.  Add "const".
            (Dominique Pelle, closes #1594)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 9782557..8755f05 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -566,7 +566,7 @@
   /* 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 int command_count = 539;
+static const int command_count = 539;
 
 /* End of automatically generated code by create_cmdidxs.pl */