SAVEQUERIES: log calling function name

[tellyworth]

The SAVEQUERIES constant tells wp-db to record SQL queries and execution time in the $wpdb->queries array. The included patch adds a third element to that array: the name of the function that called wpdb.

This makes it much easier to identify the code that caused a particular query to be run.

debug_backtrace() is PHP 4.3+, WP requires PHP 4.2+

But Thats a nice addition which will be useful to some debuggers i'm sure.. another thought is what kind of performance hit is there when using debug_backtrace()?

It's a debug method that is not enabled by default, so performance isn't such a big deal. We can do a function exists check on debug_backtrace so we don't break 4.2 users who enable this.

wpdb-get-caller-r6256-a.diff adds an is_callable() check, and fixes up the style a little.

Another place which this would be useful is the SQL Errors, It'd be nice for the SQL error messages to include the function which is running the failing SQL.

(In [6342]) Debug backtrace for queries. Props tellyworth. fixes #5218

I like this!

We should warn people about using it in production though, debug_backtrace can be SLOW.

Very great stuff! Can we have this for 2.3.2 even ?