Update elgg_query_runner() to support closures

[janlb]

While closures generally work throughout Elgg, there are some cases where their usage could cause potential problems.

Some elgg functions take a callback parameter, but they expect this parameter to be of type string.

Functions such as get_data will work if a closure is passed instead of a string, however it will also raise a PHP Notice when attempting to cast the closure to a string (and in turn generate an inaccurate "cache key")

[cash]

I'm going to change this ticket to focus on elgg_query_runner(). If there are other areas of Elgg that need to be updated for anonymous functions, please open additional tickets.

As for elgg_query_runner(), if we cannot create some sort of signature from the anonymous function, we'll have to rewrite the caching code to operate before the callback is applied.

[janlb]

Opened up a pull request ​https://github.com/Elgg/Elgg/pull/175

[Cash Costello]

Fixes #4084 support anonymous functions for db callbacks - from Janek Lasocki-Biczysko

Changeset: 2584535842eeafd8afc1b8ad40e2239fb62d015b