allow assignment to array keys @ and *; minor completion fix

tests/array27.sub

@@ -38,6 +38,13 @@ done
 
 declare -p A
 
+unset A
+declare -A A
+for k in ']' '*' '@' $'\t' ' '; do
+   A[$k]=2
+done
+declare -p A
+
 unset A
 declare -A A
 
@@ -69,4 +76,3 @@ for k in ']' '*' '@'; do
    declare "A[$k]=X"
 done
 declare -p A
-