make qw(...) first-class syntax

make qw(...) first-class syntax

This makes a qw(...) list literal a distinct token type for the
parser, where previously it was munged into a "(",THING,")" sequence.
The change means that qw(...) can't accidentally supply parens to parts
of the grammar that want real parens.  Due to many bits of code taking
advantage of that by "foreach my $x qw(...) {}", this patch also includes
a hack to coerce qw(...) to the old-style parenthesised THING, emitting
a deprecation warning along the way.