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 bug #61860: use USearch for searches, it does the right thing
small optimization
Fixed bug #65015 (pg_send_query does not flush send buffer) patch submitted by: adam at vektah dot net
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  Fixed bug #65015 (pg_send_query does not flush send buffer) patch submitted by: adam at vektah dot net
Merge branch 'PHP-5.5'

* PHP-5.5:
  Fixed bug #65015 (pg_send_query does not flush send buffer) patch submitted by: adam at vektah dot net
Update NEWS
add new test
Merge branch 'PHP-5.4' into PHP-5.5

Conflicts:
	NEWS
Merge branch 'PHP-5.5'
- Fixed test
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  - Fixed test
Merge branch 'PHP-5.5'

* PHP-5.5:
  - Fixed test
- Fixed bug #63409 (php-dba function test fails on big-endian machine) patch by: tianhonglouis at gmail dot com
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  - Fixed bug #63409 (php-dba function test fails on big-endian machine) patch by: tianhonglouis at gmail dot com
Merge branch 'PHP-5.5'

* PHP-5.5:
  - Fixed bug #63409 (php-dba function test fails on big-endian machine) patch by: tianhonglouis at gmail dot com
- Fixed bug #63983 (enabling FPM borks compile on FreeBSD) patch by: chibisuke at web dot de
- BFN
Merge branch 'PHP-5.4' into PHP-5.5

* PHP-5.4:
  - BFN
  - Fixed bug #63983 (enabling FPM borks compile on FreeBSD) patch by: chibisuke at web dot de