Bug 637852 - sasl_io_start_packet: failed - read only 3 bytes
    of sasl packet length on connection 4
    
    https://bugzilla.redhat.com/show_bug.cgi?id=637852
    
    Description: A SASL packet is made from the 4 byte length and
    the length size of payload.  When the first 4 bytes were not
    successfully received by one PR_Recv call, sasl_io_start_packet
    in sasl_io.c considered an error occurred and set PR_IO_ERROR,
    which terminates the SASL IO session.
    To give clients a chance to send the rest of the length in the
    next packet, this patch sets PR_WOULD_BLOCK_ERROR to the nspr
    error code and EWOULDBLOCK/EAGAIN to errno and once the succeeding
    packet comes in, it appends it to the previous incomplete length
    data and continues the SASL IO.