pfff: extend PHP parser to allow foo(1,2,) optional comma

Test Plan:
unit test included
make test

Reviewers: ptarjan, pieter, amenghra, zoel, julienv

Reviewed By: ptarjan

CC: jdelong

Differential Revision: https://phabricator.fb.com/D717449
* lang_php/parsing/visitor_php.ml: karguments
spatch: adhoc transfo to add trailing comma in multi line function calls

Summary: ptarjan wants that

Test Plan:
$ ~/pfff/spatch -add_trailing_comma funcall_multiline.php

 foo(1,
     2,
-    3
+    3,
    );

 foo(1,2,3);

Reviewers: ptarjan, amenghra, pieter, zoel, julienv

Differential Revision: https://phabricator.fb.com/D717468