We don't want ReflectionMethod::invoke() to simply ignore its first argument,
if the method to invoke is a static method. Instead we match its ZPP with
that of ReflectionMethod::invokeArgs(). Furthermore, we apply the DRY
principle by factoring out the code to a common helper function to prevent
inadvertent future divergence of the implementations of both methods.

As can be seen from the necessity to adapt some test cases, this causes a
BC break for some pathological cases. Therefore we apply this patch to PHP
7.1 only, which is still in beta phase.

Squashed commit of the following:

commit bdd3b6895c3ce3eacfcf7d4bf4feb8dfa61801fd
Author: Dmitry Stogov <dmitry@zend.com>
Date:   Thu Jun 16 00:19:42 2016 +0300

    Fixed GOTO VM

commit 2f1d7c8b89ce821086d357cf65f629f040a85c03
Author: Dmitry Stogov <dmitry@zend.com>
Date:   Wed Jun 15 21:01:57 2016 +0300

    Removed unused variable

commit cf749c42b0b1919f70b1e7d6dcbfff76899506af
Author: Dmitry Stogov <dmitry@zend.com>
Date:   Wed Jun 15 19:06:16 2016 +0300

    Protection from $this reassign through mb_parse_str()

commit 59a9a6c83c66b666971e57f1173b33a422166efd
Author: Dmitry Stogov <dmitry@zend.com>
Date:   Wed Jun 15 18:14:50 2016 +0300

    Added type inference rule for FETCH_THIS opcode

commit 73f8d14a856f14a461430b3c7534ab2ce870cbf6
Author: Dmitry Stogov <dmitry@zend.com>
Date:   Wed Jun 15 18:11:18 2016 +0300

    Restored PHP-7 behavior of isset($this->foo).
    It throws exception if not in object context.
    Removed useless opcode handlers.

commit fa0881381e8ae97e022ae5d1ec0851c952f33c82
Author: Dmitry Stogov <dmitry@zend.com>
Date:   Tue May 31 12:25:47 2016 +0300

    Changed "Notice: Undefined variable: this" into "Exception: Using $this when not in object context".

commit e32cc528c0f2c97963d8ec83eff0269f1f45af18
Author: Dmitry Stogov <dmitry@zend.com>
Date:   Tue May 24 02:02:43 2016 +0300

    Throw exception on attempt to re-assign $this through extract() and parse_str().

commit 41f1531b52113ec8a4c208aa6b9ef50f1386bb3f
Author: Dmitry Stogov <dmitry@zend.com>
Date:   Mon May 23 22:18:36 2016 +0300

    Fixed inconsistent $this behavior