Add connection state change events for close and open. Thanks

https://github.com/pdonald and https://github.com/maxbundchen for the
patch.

Npgsql didn't have connection state change events. According to
maxbundchen: "the EF6 depends on open/close events in some cases (like
update or insert) and Npgsql don't trigger this ones."
#19 (comment)

Added tests about those events.

src/Npgsql/NpgsqlConnection.cs

@@ -576,6 +576,9 @@ public override void Open()
 			{
 				Promotable.Enlist(Transaction.Current);
 			}
+
+            this.OnStateChange (new StateChangeEventArgs(ConnectionState.Closed, ConnectionState.Open));
+
 		}
 
 		/// <summary>
@@ -669,6 +672,9 @@ private void ReallyClose()
             }
 
             connector = null;
+
+            this.OnStateChange (new StateChangeEventArgs(ConnectionState.Open, ConnectionState.Closed));
+
         }
 
         /// <summary>

testsuite/noninteractive/NUnit20/ConnectionTests.cs

@@ -371,6 +371,37 @@ public void GetSchemaForeignKeys()
             Assert.IsNotNull(dt);
 
 
+        }
+
+        [Test]
+        public void ChangeState()
+        {
+
+            using (NpgsqlConnection c = new NpgsqlConnection (TheConnectionString)) 
+            {
+                bool stateChangeCalledForOpen = false;
+                bool stateChangeCalledForClose = false;
+
+
+                c.StateChange += new StateChangeEventHandler( delegate(object sender, StateChangeEventArgs e) {
+                    if (e.OriginalState == ConnectionState.Closed && e.CurrentState == ConnectionState.Open)
+                        stateChangeCalledForOpen = true;
+
+                    if (e.OriginalState == ConnectionState.Open && e.CurrentState == ConnectionState.Closed)
+                        stateChangeCalledForClose = true;
+                });
+
+                c.Open ();
+                c.Close ();
+
+                Assert.IsTrue (stateChangeCalledForOpen);
+                Assert.IsTrue (stateChangeCalledForClose);
+
+            }
+
+
+
+
         }
 
     }