sgrep: fix FakeTok exception when a metavariable matches a lambda.

Summary: Elliot found this bug.

Test Plan:
$ ~/pfff/sgrep -e 'self::stubOutFunction(X, Y)' flib/account/creation/partial/__tests__/PartialAccountCreatorTestCase.php
flib/account/creation/partial/__tests__/PartialAccountCreatorTestCase.php:38
     self::stubOutFunction(
       'PartialAccountConfirmationManager::genIsValidCode',
       function (string $code) {
         yield result(true);
       }
     );

which works as intented.

Reviewers: pieter, amenghra

Reviewed By: pieter

CC: elynde

Differential Revision: https://phabricator.fb.com/D678419

Task ID: 2019728
* h_program-lang/dependencies_matrix_code.ml: refactoring
* h_program-lang/dependencies_matrix_code.ml: try pack entries in ..., part 1