Fixed Mention.GetUserIds, dont mention the same user multiple times.

src/Discord.Net/DiscordClient.Messages.cs

@@ -119,7 +119,7 @@ namespace Discord
 		private async Task<Message> SendMessage(Channel channel, string text, bool isTextToSpeech)
 		{
 			Message msg;
-			var userIds = !channel.IsPrivate ? Mention.GetUserIds(text) : new string[0];
+			var userIds = !channel.IsPrivate ? Mention.GetUserIds(text).Distinct() : new string[0];
 			if (Config.UseMessageQueue)
 			{
 				var nonce = GenerateNonce();

src/Discord.Net/Helpers/Mention.cs

@@ -6,8 +6,8 @@ namespace Discord
 {
     public static class Mention
 	{
-		private static readonly Regex _userRegex = new Regex(@"<@(?:[0-9]+?)>", RegexOptions.Compiled);
-		private static readonly Regex _channelRegex = new Regex(@"<#(?:[0-9]+?)>", RegexOptions.Compiled);
+		private static readonly Regex _userRegex = new Regex(@"<@([0-9]+?)>", RegexOptions.Compiled);
+		private static readonly Regex _channelRegex = new Regex(@"<#([0-9]+?)>", RegexOptions.Compiled);
 
 		/// <summary> Returns the string used to create a user mention. </summary>
 		public static string User(User user)