add log messages, to make some problems being debugged easier to see

src/echo_api.c

@@ -416,7 +416,7 @@ static PEP_STATUS echo_challenge_for_identity(PEP_SESSION session,
     sql_status = pEp_sqlite3_step_nonbusy(session, session->echo_get_challenge);
     ON_SQL_ERROR_SET_STATUS_AND_GOTO;
     if (sql_status != SQLITE_ROW)
-        LOG_ERROR("foo!");
+        LOG_NONOK("did not find echo challenge for %s <%s>: sql_status %i", (identity->username ? identity->username : "NOUSERNAME"), (identity->address ? identity->address : "NOADDRESS"), sql_status);
     const void *stored_challenge;
     if (sql_status == SQLITE_DONE) /* no row found: no user_id?  This will
                                       never happen in sane situations.  It

src/message_api.c

@@ -5858,6 +5858,7 @@ static PEP_STATUS _decrypt_message(
                             
                         }
                         else { // should never happen
+                            LOG_ERROR("THIS MUST NOT HAPPEN -- but I have seen it happen in the Engine test suite with pEpMIME aaofghjfgkh");
                             status = PEP_UNKNOWN_ERROR;
                             free_message(inner_message);
                             goto pEp_error;