int libssh2_session_set_last_error(LIBSSH2_SESSION *session, int errcode, const char *errmsg)
errcode - One of the error codes as defined in the public libssh2 header file.
errmsg - If not NULL, a copy of the given string is stored inside the session object as the error message.
This function is provided for high level language wrappers (i.e. Python or Perl) and other libraries that may extend libssh2 with additional features while still relying on its error reporting mechanism.