Postfix dereference syntax

$_->$* means $$_ (and compiled down to the same op tree)
$_->@* means @$_ ( ditto ditto blah blah blah          )
$_->%* means %$_ (...)
$_->&* means &$_
$_->** means *$_
$_->@[...] means @$_[...]
$_->@{...} means @$_{...}
$_->*{...} means *$_{...}

$_->@* is not always equivalent to @$_, particularly in contexts like
@foo[0], which cannot be written foo->@*[0].  (Just omit the asterisk
and it works.)
Tests for postfix dereference
Add postfixderef.t to MANIFEST
Fix up postfixderef.t