Issue #19030: final pieces for proper location of various class attributes located in the metaclass.

Okay, hopefully the very last patch for this issue.  :/

I realized when playing with Enum that the metaclass attributes weren't always displayed properly.

New patch properly locates DynamicClassAttributes, virtual class attributes (returned by __getattr__ and friends), and metaclass class attributes (if they are also in the metaclass __dir__ method).

Also had to change one line in pydoc to get this to work.

Added tests in test_inspect and test_pydoc to cover these situations.

those in the same process group.

limiting the call to readline().  Original patch by Michał
Jastrzębski and Giampaolo Rodola.

limiting the call to readline().  Original patch by Michał
Jastrzębski and Giampaolo Rodola.

Eliminates a refleak introduced in commit b4a325275fb0

This should supersede revision e3ec6b17260c (but please test before removing that).