Fix: add missing declarations to context.h

This is mostly to be able to access it in the test suite following this
commit.
Signed-off-by: David Goulet <dgoulet@ev0ke.net>
Signed-off-by: Ian Goldberg <iang@cs.uwaterloo.ca>

src/context.h

@@ -180,4 +180,13 @@ int otrl_context_forget(ConnContext *context);
 /* Forget all the contexts in a given OtrlUserState. */
 void otrl_context_forget_all(OtrlUserState us);
 
+/* Find requested recent instance */
+ConnContext * otrl_context_find_recent_instance(ConnContext * context,
+		otrl_instag_t recent_instag);
+
+/* Find the instance of this context that has the best security level, and for
+ * which we have most recently received a message from. Note that most recent
+ * in this case is limited to a one-second resolution. */
+ConnContext * otrl_context_find_recent_secure_instance(ConnContext * context);
+
 #endif