gio: Make minor docs improvements

This commit changes a comment in _g_dbus_worker_do_read_cb() to be
slightly more useful. At least in my experience debugging an
intermittent unit test failure in another project, this failure
condition occurred because although g_test_dbus_down() ensures that the
session GDBusConnection has exit-on-close set to FALSE before killing
its dbus-daemon, there was still a GDBusConnection on the system bus
which hit this failed read code path, because we had
DBUS_SYSTEM_BUS_ADDRESS set to the address of the #GTestDBus daemon, to
appease libudisks.

Also, make a few other minor improvements to the docs.

gio/gdbusconnection.c

@@ -128,7 +128,7 @@
  * The #GDBusConnection type is used for D-Bus connections to remote
  * peers such as a message buses. It is a low-level API that offers a
  * lot of flexibility. For instance, it lets you establish a connection
- * over any transport that can by represented as an #GIOStream.
+ * over any transport that can by represented as a #GIOStream.
  *
  * This class is rarely used directly in D-Bus clients. If you are writing
  * a D-Bus client, it is often easier to use the g_bus_own_name(),
@@ -2968,8 +2968,8 @@ g_dbus_connection_new_for_address_sync (const gchar           *address,
  * more details.
  *
  * Note that this function should be used with care. Most modern UNIX
- * desktops tie the notion of a user session the session bus, and expect
- * all of a users applications to quit when their bus connection goes away.
+ * desktops tie the notion of a user session with the session bus, and expect
+ * all of a user's applications to quit when their bus connection goes away.
  * If you are setting @exit_on_close to %FALSE for the shared session
  * bus connection, you should make sure that your application exits
  * when the user session ends.
@@ -7364,7 +7364,7 @@ bus_get_async_initable_cb (GObject      *source_object,
  * When the operation is finished, @callback will be invoked. You can
  * then call g_bus_get_finish() to get the result of the operation.
  *
- * This is a asynchronous failable function. See g_bus_get_sync() for
+ * This is an asynchronous failable function. See g_bus_get_sync() for
  * the synchronous version.
  *
  * Since: 2.26

gio/gdbusprivate.c

@@ -701,7 +701,7 @@ _g_dbus_worker_do_read_cb (GInputStream  *input_stream,
            worker);
 #endif
 
-  /* TODO: hmm, hmm... */
+  /* The read failed, which could mean the dbus-daemon was sent SIGTERM. */
   if (bytes_read == 0)
     {
       g_set_error (&error,

gio/gtestdbus.c

@@ -801,7 +801,7 @@ g_test_dbus_stop (GTestDBus *self)
  * Stop the session bus started by g_test_dbus_up().
  *
  * This will wait for the singleton returned by g_bus_get() or g_bus_get_sync()
- * is destroyed. This is done to ensure that the next unit test won't get a
+ * to be destroyed. This is done to ensure that the next unit test won't get a
  * leaked singleton from this test.
  */
 void