Modules: add RM_Replicate() Tcl test file & fix the module.

tests/unit/moduleapi/propagate.tcl

@@ -0,0 +1,30 @@
+set testmodule [file normalize tests/modules/propagate.so]
+
+tags "modules" {
+    test {Modules can propagate in async and threaded contexts} {
+        start_server {} {
+            set replica [srv 0 client]
+            set replica_host [srv 0 host]
+            set replica_port [srv 0 port]
+            start_server [list overrides [list loadmodule "$testmodule"]] {
+                set master [srv 0 client]
+                set master_host [srv 0 host]
+                set master_port [srv 0 port]
+
+                # Start the replication process...
+                $replica replicaof $master_host $master_port
+                wait_for_sync $replica
+
+                after 1000
+                $master propagate-test
+
+                wait_for_condition 5000 10 {
+                    ([$replica get timer] eq "10") && \
+                    ([$replica get thread] eq "10")
+                } else {
+                    fail "The two counters don't match the expected value."
+                }
+            }
+        }
+    }
+}