Reduce used window sizes by factor 10

As reported in bug report #166 http://libssh2.stuge.se/ticket/166
by 'ptjm', the maximum window size must be less crazy for libssh2
to do better with more server implementations. I did not do any
testing to see how this changes raw SCP performance, but the
maximum window size is still almost 4MB. This also has the upside
that libssh2 will use less memory.

src/channel.c

@@ -1821,7 +1821,7 @@ ssize_t _libssh2_channel_read(LIBSSH2_CHANNEL *channel, int stream_id,
            more off the network again */
         channel->read_state = libssh2_NB_state_created;
 
-    if(channel->remote.window_size < (LIBSSH2_CHANNEL_WINDOW_DEFAULT*300)) {
+    if(channel->remote.window_size < (LIBSSH2_CHANNEL_WINDOW_DEFAULT*30)) {
         /* the window is getting too narrow, expand it! */
 
       channel_read_ex_point1:
@@ -1829,7 +1829,7 @@ ssize_t _libssh2_channel_read(LIBSSH2_CHANNEL *channel, int stream_id,
         /* the actual window adjusting may not finish so we need to deal with
            this special state here */
         rc = _libssh2_channel_receive_window_adjust(channel,
-                                                    (LIBSSH2_CHANNEL_WINDOW_DEFAULT*600), 0, NULL);
+                                                    (LIBSSH2_CHANNEL_WINDOW_DEFAULT*60), 0, NULL);
         if (rc == PACKET_EAGAIN)
             return rc;