This lets a subclass override it

* cleanup session temp file

* Fix Deprecated: Automatic conversion of false to array

* New option 'database' for Redis class constructor

Selecting database is very common action after connecting to Redis. This simplifies lazy connecting to Redis, when requested database will be selected after first command.

* More specific exception message when invalid auth or database number is provided

Before it was just 'Redis server went away'

* Rename reselect_db method to redis_select_db and slightly optimise it

* Refactor `getWithMeta`

* Consolidate `getWithMeta()` test.

* Review comments

This method always unpack given string to zval, so it is not necessary to check output value

Deduplicate code that is used in many methods. Also optimise adding new element to array in pipeline mode and returning zval in atomic mode

Same fix as 6e5360d, with PHP switching from `ZEND_ASSUME` to `ZEND_ASSERT` in zend_hash_str_update_ptr.

Fixes #2648

`Redis::hGetAll()` returns an array indexed by `string`s and/or `int`s depending on the values in the hash set.

The function in the PHP stub was annotated as though the array were keyed only by strings, which is tighter than reality.