Make __DATA__ use the right pkg

Make __DATA__ use the right pkg

__DATA__ is supposed to stuff the rest of the file into the DATA han-
dle belonging to the package in scope where __DATA__ is encountered.
That means this should always print 123:

print <DATA>;
__DATA__
123

But it fails if the package has been renamed through glob assignment:

package foo;
BEGIN{*foo::=*bar::}
print <DATA>;
__DATA__
123

(Prints nothing.)

The code for stuffing DATA was stringifying the package and then look-
ing it up again.  Not only is it more correct to avoid the stringifi-
cation, but faster, too.