Issue #16133: The asynchat.async_chat.handle_read() method now ignores
BlockingIOError exceptions. Initial patch written by Xavier de Gaye.

Document also in asyncore documentation that recv() may raise BlockingIOError.
(Merge 3.4) Issue #16133: The asynchat.async_chat.handle_read() method now
ignores BlockingIOError exceptions. Initial patch written by Xavier de Gaye.

Document also in asyncore documentation that recv() may raise BlockingIOError.