prolog: add unit test showing uses of docall and new Xxx()

Test Plan: ./codequery -test

Reviewers: bill, pieter, jyan

Reviewed By: pieter

Differential Revision: https://phabricator.fb.com/D763597
prolog: handling the new PHP syntax for (new Xxx())->foo()

Summary:
Jyan detected bugs in cmf --prolog where some calls to new
were not present in the prolog DB. It's because of the
new construct in ast_php.ml which was not take into account
in the prolog fact generator. This patch fixes that.

thx jyan.

Test Plan:
unit test included
$ make test

Reviewers: bill, pieter, zoel, jyan

Reviewed By: pieter

CC: ptarjan, julienv, amenghra

Differential Revision: https://phabricator.fb.com/D763650
prolog: basic support for class constants use

Summary: jyan wanted that

Test Plan:
unit test included
$ make test

Reviewers: jyan, bill, pieter, zoel

Reviewed By: pieter

CC: amenghra, julienv

Differential Revision: https://phabricator.fb.com/D763732

Task ID: 2254123
Merge branch 'master' of github.com:facebook/pfff
Merge branch 'master' of github.com:facebook/pfff
* tests/php/scheck/xhp.php:
* commons/common2.ml: revert zoe, make test was failing in cmf