Patch for multiple buckets breaks module loading

The core patch to allow fields to specify particular buckets causes module loading to become very fragile when the module implements cache can't be relied upon.

"But IslandUsurper, when would that cache be unreliable?"

When you're copying over a database from one site to another, and the modules are installed and core has been patched, then the bootstrap and implementation cache isn't warmed up.

As I mentioned in #1925922-166: Unsupported operand types in factory_by_row() in flag_flag.inc, I found a spot where file_scan_directory() gets called before all of the modules have been loaded. But that's a special case, and not everyone uses filefield_paths. However I found another place today, because the same problem showed up again. It's in system_list(). Which is called by module_load_all(). So, with the patch for image styles and a completely fresh cache, it's really hard to get hook implementations loaded.

Fortunately, I don't think I need this patch, so I can just unapply the patch. But I don't see how we can get everything we want.