Add ssh_callbacks_exists internal macro + unittest

(first commit with eclipse helios, crossing fingers ...)

tests/unittests/torture_callbacks.c

@@ -0,0 +1,61 @@
+#define LIBSSH_STATIC
+
+#include "torture.h"
+#include <libssh/priv.h>
+#include <libssh/callbacks.h>
+
+static int myauthcallback (const char *prompt, char *buf, size_t len,
+    int echo, int verify, void *userdata){
+	(void) prompt;
+	(void) buf;
+	(void) len;
+	(void) echo;
+	(void) verify;
+	(void) userdata;
+	return 0;
+}
+
+struct ssh_callbacks_struct callbacks =
+{
+		.userdata=(void *)0x0badc0de,
+		.auth_function=myauthcallback
+};
+
+static void setup(void) {
+	ssh_callbacks_init(&callbacks);
+}
+
+static void teardown(void) {
+
+}
+
+START_TEST (torture_callbacks_size)
+{
+	ck_assert_int_ne(callbacks.size,0);
+}
+END_TEST
+
+START_TEST (torture_callbacks_exists)
+{
+	ck_assert_int_ne(ssh_callbacks_exists(&callbacks,auth_function),0);
+	ck_assert_int_eq(ssh_callbacks_exists(&callbacks,log_function),0);
+	/* we redefine size so auth_function is outside the range of callbacks->size */
+  callbacks.size=(unsigned char *)&(callbacks.auth_function) - (unsigned char *)&callbacks;
+  ck_assert_int_eq(ssh_callbacks_exists(&callbacks,auth_function),0);
+  /* now make it one pointer bigger so we spill over the auth_function slot */
+  callbacks.size += sizeof(void *);
+  ck_assert_int_ne(ssh_callbacks_exists(&callbacks,auth_function),0);
+}
+END_TEST
+
+Suite *torture_make_suite(void) {
+  Suite *s = suite_create("libssh_options");
+
+  torture_create_case_fixture(s, "torture_callbacks_size",
+          torture_callbacks_size, setup, teardown);
+  torture_create_case_fixture(s, "torture_callbacks_exists",
+          torture_callbacks_exists, setup, teardown);
+
+  return s;
+}
+