ZODB Components: Resetting Portal Type classes was also clearing Interfaces of...

ZODB Components: Resetting Portal Type classes was also clearing Interfaces of erp5.component.* modules.

__implemented__ and __provides__ attributes are cleared on Portal Type reset
to break a circular reference (11e2b506). Resetting of ZODB Components is
done independently of Portal Type classes, so until the next ZODB Component
reset, Interfaces were not implemented anymore.

11e2b506 states that this creates a memory leak but this is not actually true
as Python garbage collector will break such circular reference and collect
this object, as asserted by a newly introduced Unit Test. This is probably
less efficient than explicitly breaking the circular reference and thus relies
on reference counting (rather than the garbage collector) but doing otherwise
would require introspecting ZODB Components module to find classes implementing
Interfaces (erp5.portal_type only contains classes).

This only takes care of ZODB Components modules but maybe breaking circular
references for Portal Type classes is not even needed (if so, this will be done
in a later commit).