more changes to avoid expanding associative array subscripts twice; internal debugging changes

doc/bash.1

@@ -9953,7 +9953,9 @@ Exit after reading and executing one command.
 .TP 8
 .B \-u
 Treat unset variables and parameters other than the special
-parameters "@" and "*" as an error when performing
+parameters "@" and "*",
+or array variables subscripted with "@" or "*",
+as an error when performing
 parameter expansion.  If expansion is attempted on an
 unset variable or parameter, the shell prints an error message, and,
 if not interactive, exits with a non-zero status.