Improve extra ex_data parameter of server callback functions

[DDvO]

I came across the last parameter 'ex_data' of the server callback functions:

int (*est_enroll_pkcs10_cb)(unsigned char *pkcs10, int p10_len, 
                        unsigned char **pkcs7, int *cert_len,
            char *user_id, X509 *peer_cert,
            void *ex_data);
int (*est_reenroll_pkcs10_cb)(unsigned char *pkcs10, int p10_len, 
                          unsigned char **pkcs7, int *cert_len,
              char *user_id, X509 *peer_cert,
              void *ex_data);
unsigned char *(*est_get_csr_cb)(int *csr_len, void *ex_data);
int (*est_http_auth_cb)(struct est_ctx *ctx, EST_HTTP_AUTH_HDR *ah, 
                    X509 *peer_cert, void *ex_data);

partially documented at the est_set_ex_data() function declaration in est.c .

I suggest completing its documentation in est_server.c and est_locl.h and removing its test use in estserver.c, as done tentatively in the diff I'm going to provide,

[jfigus]

Rather than providing a diff, the suggested work-flow for contributing code is:

1. Fork the branch in github
2. Make the changes to your local fork
3. Submit a pull request to contribute your changes back to the libest branch that you forked

[jfigus]

Closing issue, still have not see a pull request with the proposed fix.

[DDvO]

The suggested improvements have been included, among many others, in the set of changes provided on March 20th.