sgrep/spatch: allow 'new X()' to match 'new $xx()' or 'new self()'

Summary: paul found those bugs.

Test Plan:
./sgrep -test
also
$ ~/pfff/sgrep -e 'new X(...)' new_var.php
new_var.php:3
 $o = new Foo();
new_var.php:7
     $o = new self();
new_var.php:11
 $o = new $dyn(1);

Reviewers: pieter, julienv, amenghra, ptarjan

Reviewed By: pieter

CC: zoel, lisp

Differential Revision: https://phabricator.fb.com/D739439