store agrcache's file data in a custom table

The custom table is missing indexes - at least needs an index on file type and could use a primary key as well.

Would it be worth caching the files on get - would save a couple of database hits each page when using the alternative cache storage.

The cache_clear_all() call was missing an explicit cache bin.

Otherwise this works well for me.

Actually discovered an issue where the file list was updating for the 'footer' scope, then being fully overwritten by the 'header' scope later within the same request. This prevented 'footer' from every being preserved in the database. I've changed the logic so that

I believe the merge operation here actually creates a possibility for a race condition. Since a cache_get() followed by the array_merge(), any changes to the agrcache array between these operations could result in lost files. This implementation will reduce that, but without locking it's still possible.

I refactored this slightly so that, rather than relying on an existing array structure in the database, the module can be more resilient if the database table is empty. This also means we can remove the custom INSERTs at install.

Accidentally added the d.o .info snippet

Until variable_set() stampedes are fixed/mitigated in core, treating this as an agrcache bug.

The update should not use the schema API but specify the table definition directly, re-rolled for that and a conflict.

Another update - the watchdog warning happens straight after updating the module, changed to a notice.

And db_update() instead of db_query('UPDATE...

With that, this is testing OK. Committed/pushed to 7.x-1.x, thanks!