Treat calls to gen_server:call/2 and gen_server2:call/2 as errors.

check_xref

@@ -136,6 +136,14 @@ checks() ->
         error, filters()},
     {"(Lin) (L - LU)", "has unused local function(s)",
         error, filters()},
+    %% E  - all edges (i.e. function calls)
+    %% |  - calling from
+    %% || - calling to
+    %% "RE1" : "RE2" / "RE3" - regex MFA
+    {"(E | \"(rabbit|amqp).*\" : \".*\" / \".*\" || "
+     "\"gen_server2?\" : \"call\" / \"2\")",
+     "5 sec timeout in",
+     error, filters()},
     {"(Lin) (LU * (X - XU))",
         "has exported function(s) only used locally",
         warning, filters()},