added bases for nonblocking packet sending and receiving. packet_send

and packet_read may return SSH_AGAIN if the session is nonblocking and 
there is not enough data to be read.
I also added a socket buffering through session->in_socket_buffer. It is 
more low-level than the packet buffer.
I should rename in_buffer with in_packet_buffer.
There is still work to do with the socket status, (opened, error, 
closed, ...) and much more work to extend the nonblocking to session 
opening, messages sending and such.
I find the switch(session->packet_state) solution very nice (especially 
when the nonblocking function may have 10 differents states, like in a 
connection.)


git-svn-id: svn+ssh://svn.berlios.de/svnroot/repos/libssh/trunk@49 7dcaeef0-15fb-0310-b436-a5af3365683c

include/libssh/libssh.h

@@ -90,6 +90,10 @@ typedef uint8_t u8;
 #define SSH_FATAL 2
 #define SSH_EINTR 3
 
+/* error return codes */
+#define SSH_OK 0     /* No error */
+#define SSH_ERROR -1 /* error of some kind */
+#define SSH_AGAIN 1  /* the nonblocking call must be repeated */
 
 char *ssh_get_error(void *error); 
 int ssh_get_error_code(void *error);