fix CSHARP-102

Sample code:
```
var command = table.Insert(new NerdMovie { Year = 2005, Director = "Quentin Tarantino", Movie = "Pulp Fiction", Maker = "Pixar" }).SetTimestamp(DateTime.Now);
Console.WriteLine(command);
```

Produces output
```
INSERT INTO "nerdiStuff"("diri", "When-Made", "movieTile", "movieMaker", "List") VALUES ('Quentin Tarantino', 2005, 'Pulp Fiction', 'Pixar', []) USING TIMESTAMP 1396617880926
```

the timestamp is in milliseconds but according to CQL reference http://cassandra.apache.org/doc/cql3/CQL.html#updateStmt insert and update statements should be in microseconds
```
TIMESTAMP: sets the timestamp for the operation. If not specified, the current time of the insertion (in microseconds) is used. This is usually a suitable default.
```

Such behavior complicates updating data if it was inserted without explicitly defining timestamp. The following example outputs 2005 but the expected value is 2006
```
table.Insert(
	new NerdMovie 
	{ 
		Year = 2005, 
		Director = "Quentin Tarantino", 
		Movie = "Pulp Fiction", 
		Maker = "Pixar" 
	}).Execute();
Thread.Sleep(60*1000);	//sleep one minute just in case cassandra's and client's clocks are not in sync. In current test both client and cassandra resides on same machine
table
	.Where(m => 
		m.Movie == "Pulp Fiction" 
		&& m.Maker=="Pixar" 
		&& m.Director == "Quentin Tarantino")
	.Select(m => new NerdMovie { Year = 2006 })
	.Update()
	.SetTimestamp(DateTime.Now)
	.Execute();

Console.WriteLine(
	table
		.Where(m => 
			m.Movie == "Pulp Fiction" 
			&& m.Maker=="Pixar" 
			&& m.Director == "Quentin Tarantino")
		.Execute()
		.FirstOrDefault()
		.Year);
```