Major overhaul of timeout sockets:

- setblocking(0) and settimeout(0) are now equivalent, and ditto for
  setblocking(1) and settimeout(None).

- Don't raise an exception from internal_select(); let the final call
  report the error (this means you will get an EAGAIN error instead of
  an ETIMEDOUT error -- I don't care).

- Move the select to inside the Py_{BEGIN,END}_ALLOW_THREADS brackets,
  so other theads can run (this was a bug in the original code).

- Redid the retry logic in connect() and connect_ex() to avoid masking
  errors.  This probably doesn't work for Windows yet; I'll fix that
  next.  It may also fail on other platforms, depending on what
  retrying a connect does; I need help with this.

- Get rid of the retry logic in accept().  I don't think it was needed
  at all.  But I may be wrong.

Doc/lib/libsocket.tex

@@ -72,8 +72,9 @@ argument types and out-of-memory conditions can be raised; errors
 related to socket or address semantics raise the error
 \exception{socket.error}.
 
-Non-blocking mode is supported through the
-\method{setblocking()} method.
+Non-blocking mode is supported through
+\method{setblocking()}.  A generalization of this based on timeouts
+is supported through \method{settimeout()}.
 
 The module \module{socket} exports the following constants and functions:
 
@@ -284,8 +285,7 @@ checked --- subsequent operations on the object may fail if the file
 descriptor is invalid.  This function is rarely needed, but can be
 used to get or set socket options on a socket passed to a program as
 standard input or output (such as a server started by the \UNIX{} inet
-daemon).  The socket is assumed to be in blocking mode without
-a timeout.
+daemon).  The socket is assumed to be in blocking mode.
 Availability: \UNIX.
 \end{funcdesc}
 
@@ -514,38 +514,39 @@ all sockets are in blocking mode.  In non-blocking mode, if a
 \method{send()} call can't immediately dispose of the data, a
 \exception{error} exception is raised; in blocking mode, the calls
 block until they can proceed.
+\code{s.setblocking(0)} is equivalent to \code{s.settimeout(0)};
+\code{s.setblocking(1)} is equivalent to \code{s.settimeout(None)}.
 \end{methoddesc}
 
 \begin{methoddesc}[socket]{settimeout}{value}
-Set a timeout on blocking socket operations. Value can be a
-nonnegative float expressing seconds, or \code{None}.  If a float is
+Set a timeout on blocking socket operations.  The \var{value} argument
+can be a nonnegative float expressing seconds, or \code{None}.
+If a float is
 given, subsequent socket operations will raise an \exception{error}
 exception if the timeout period \var{value} has elapsed before the
 operation has completed.  Setting a timeout of \code{None} disables
 timeouts on socket operations.
+\code{s.settimeout(0.0)} is equivalent to \code{s.blocking(0)};
+\code{s.settimeout(None)} is equivalent to \code{s.setblocking(1)}.
 \versionadded{2.3}
 \end{methoddesc}
 
 \begin{methoddesc}[socket]{gettimeout}{}
 Returns the timeout in floating seconds associated with socket
-operations, or \code{None} if no timeout is set.
+operations, or \code{None} if no timeout is set.  This reflects
+the last call to \method{setblocking()} or \method{settimeout()}.
 \versionadded{2.3}
 \end{methoddesc}
 
-Some notes on the interaction between socket blocking and timeouts: A
-socket object can be in one of three modes: blocking, non-blocking, or
-timout.  Sockets are always created in blocking mode.  In blocking
-mode, operations block until complete.  In non-blocking mode,
-operations fail (with an error that is unfortunately system-dependent)
-if they cannot be completed immediately.  In timeout mode, operations
-fail if they cannot be completed within the timeout specified for the
-socket.
-
-Calling \method{settimeout()} cancels non-blocking mode as set by
-\method{setblocking()}; calling \method{setblocking()} cancels a
-previously set timeout.  Setting the timeout to zero acts similarly
-but is implemented different than setting the socket in non-blocking
-mode (this could be considered a bug and may even be fixed).
+Some notes on socket blocking and timeouts: A socket object can be in
+one of three modes: blocking, non-blocking, or timout.  Sockets are
+always created in blocking mode.  In blocking mode, operations block
+until complete.  In non-blocking mode, operations fail (with an error
+that is unfortunately system-dependent) if they cannot be completed
+immediately.  In timeout mode, operations fail if they cannot be
+completed within the timeout specified for the socket.  The
+\method{setblocking()} method is simply a shorthand for certain
+\method{settimeout()} calls.
 
 Timeout mode internally sets the socket in non-blocking mode.  The
 blocking and timeout modes are shared between file descriptors and