Add create_sid to session_set_save_handler and SessionHandler

A lot of code already existed to allow a custom create_sid handler, but
lacked a specific implementation.

Therefore I have added a 7th (optional) argument
session_set_save_handler, to allow a user function to be supplied for
session id generation.

If a create_sid function is not supplied, the default function is
called in its absence to preserve backwards compatibility.

Likewise create_sid only added to SessionHandler class, and not the
interface to maintain backwards compatibility. If the result is not
overridden, the default is called.
Tests, fixes and optimisations

* Amended existing tests to cater for new functionality.
* Implemented fixes and optimisations recommended by NikiC
* Added create_sid to the registered interface. This was breaking
tests. It also now breaks BC for people implementing the interface
directly instead of extending the class.
fix BELL constant declaration
fix coverage data for the opcache optimizer
Fixed issue #79 (Optimization Problem/Bug)
Fix test
Merge branch 'PHP-5.3' into PHP-5.4
Merge branch 'PHP-5.4' into PHP-5.5
Fixed bug parameter is casted to string of array_column
Fixed ZTS build
Fixed Bug #64565 copy doesn't report failure on partial copy

_php_stream_copy_to_stream_ex, when mmap is possible, doesn't check
if actually written bytes match read bytes.

Fix this (paranoid check) to be consistent with non mmap mode

Seems hard to add a unit test, as this rely on a full filesystem.
fix comment
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  fix comment
  Fixed Bug #64565 copy doesn't report failure on partial copy
keep previous test to avoid any behavior change
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  keep previous test to avoid any behavior change
NEW for #64565
NEW for #64565
Add CURL_WRAPPERS_ENABLE constant

see http://news.php.net/php.internals/66871
Merge branch 'PHP-5.4' of git.php.net:php-src into PHP-5.4
Use new constant replace ugly trick