Compiling docs/examples/sessioninfo.c

[gvanem]

Compiling this example, gives some warnings:

sessioninfo.c(62,34): warning: implicit declaration of function 'gnutls_x509_crt_init' is invalid in C99
      [-Wimplicit-function-declaration]
          if(GNUTLS_E_SUCCESS == gnutls_x509_crt_init(&cert)) {
                                 ^
sessioninfo.c(64,16): warning: implicit declaration of function 'gnutls_x509_crt_import' is invalid in C99
      [-Wimplicit-function-declaration]
               gnutls_x509_crt_import(cert, &chainp[i], GNUTLS_X509_FMT_DER)) {
               ^
...

I suggest we simply do like in vtls/gtls.c:

--- a/sessioninfo.c 2019-12-09 13:44:40
+++ b/sessioninfo.c 2020-03-31 11:49:52
@@ -31,6 +31,7 @@

 #include <curl/curl.h>
 #include <gnutls/gnutls.h>
+#include <gnutls/x509.h>

[bagder]

Thanks!