fix problem with saving tty state after running a command with 'bind -x'; builtins that create associative arrays can now convert existing scalar variables to associative arrays

doc/bashref.texi

@@ -7701,6 +7701,9 @@ interpreted as relative to one greater than the maximum index of
 @var{name}, so negative indices count back from the end of the
 array, and an index of -1 references the last element.
 
+The @samp{+=} operator will append to a array variable when assigning
+using the compound assignment syntax; see @ref{Shell Parameters} above.
+
 Any element of an array may be referenced using
 @code{$@{@var{name}[@var{subscript}]@}}.
 The braces are required to avoid