.c files only need to import psycopg.h: it will in turn import
dependencies from Python and libpq and configure.h. psycopg.h should be
the first to be imported, so the basic imports are not required in
the .h's
As a guideline I'm trying to import from the most specific to the most
generic to detect missing imports in the .h's.
Do it by keeping the reference to the last PGresult in the cursor and
calling pq_fetch() before ending the asynchronous execution. This
takes care of handling the possible error state of the PGresult and
also allows the removal of the needsfetch flag, since now after
execution ends the results are already fetched and parsed.
Without this a query that did not get flushed completely to the server
would cause cursor.poll() to always go into the curs_poll_send()
branch even if it was retuning ASYNC_READ.
Bug report by Daniele Varrazzo.
POLL_OK has been changed from 3 to 0 to let the user specify a short loop
just as "if not curs.poll()" instead of having to check for write and read
separately. For an example of this, see examples/notify.py.
It was trying to get all pending results from the connection and if
the client sent many and anyone except the first one would not be
immediately available the loop in curs_get_last_result would call
PQgetResult blockingly.
Avoid that by calling PQisBusy every time and telling the client to
wait for more data if it returns 1.
The isread() API was not safe, because the query might have not been
sent fully to the server after calling execute(). To make the async
API complete, a similar mechanism to async connections must be used.
The cursor now has a poll() method that you would use identically to
the poll() method of the connection class.
