Use aver not assert.

* src/output.c: Don't include assert.h.
(output_skeleton): Use aver not assert.
* src/system.h (aver): In documentation of why, add links to
Paul Eggert's explanations in the mailing lists.

src/output.c

@@ -21,7 +21,6 @@
 #include <config.h>
 #include "system.h"
 
-#include <assert.h>
 #include <configmake.h>
 #include <error.h>
 #include <get-errno.h>
@@ -637,7 +636,7 @@ output_skeleton (void)
     argv[i++] = full_m4bison;
     argv[i++] = full_skeleton;
     argv[i++] = NULL;
-    assert (i <= ARRAY_CARDINALITY (argv));
+    aver (i <= ARRAY_CARDINALITY (argv));
   }
 
   init_subpipe ();