Clean field_attach_* namespace

field_attach_* functions are the "functions that fieldable entities need to call at the right time in their own workflow in order to call themselves fieldable:
f_a_load(), f_a_presave(), f_a_insert()...". They are listed on http://api.drupal.org/api/group/field_attach/7, which lets developpers have a cleaner view of " what do I need to do to be fieldable ? is there any f_a_*() function I have forgotten ?".

There are currently 3 exceptions; field_attach_extract_ids(), field_attach_extract_bundle(), field_attach_create_stub_object(), are just generic helper functions that 'fieldable entity' modules shouldn't actually need to call.

Those 3 functions should be moved back to field.module file, and renamed field_extract_ids(), field_extract_bundle(), field_create_stub_entity()
Obviously, all existing calls to those functions should be renamed too.