This is a measure to support form fields and controllers
interacting with files in different contexts,
for example an UploadField used in a ModelAdmin,
or a website frontend. The check for 'CMS_ACCESS_AssetAdmin'
was too restricting. This wasn't a problem in 2.x simply because
the old FileField/Upload classes didn't respect File->can*()
permissions.
Use third party tools like XHProf instead.
Removed defunct or unnecessary debug GET parameters:
debug_profile, debug_memory, profile_trace, debug_javascript, debug_behaviour
