(chocolatey#1764) source exit 2 if nothing to do

If enhanced exit codes are enabled, this sets the source command to
exit with 2 if there is nothing to do (i.e. if NOCHANGEMESSAGE is
output).

src/chocolatey/infrastructure.app/commands/ChocolateySourceCommand.cs

@@ -160,12 +160,17 @@ Exit codes that normally result from running this command.
 Normal:
  - 0: operation was successful, no issues detected
  - -1 or 1: an error has occurred
+ - 2: nothing to do (enhanced)
+
+NOTE: Starting in v0.10.12, if you have the feature '{0}' 
+ turned on, then choco will provide enhanced exit codes that allow 
+ better integration and scripting.
 
 If you find other exit codes that we have not yet documented, please
  file a ticket so we can document it at
  https://github.com/chocolatey/choco/issues/new/choose.
 
-");
+".format_with(ApplicationParameters.Features.UseEnhancedExitCodes));
 
             "chocolatey".Log().Info(ChocolateyLoggers.Important, "Options and Switches");
         }

src/chocolatey/infrastructure.app/services/ChocolateyConfigSettingsService.cs

@@ -151,6 +151,11 @@ public void AddSource(ChocolateyConfiguration configuration)
                     )
                 {
                     if (!configuration.QuietOutput) this.Log().Warn(NoChangeMessage);
+
+                    if (configuration.Features.UseEnhancedExitCodes && Environment.ExitCode == 0)
+                    {
+                        Environment.ExitCode = 2;
+                    }
                 }
                 else
                 {
@@ -183,6 +188,11 @@ public void RemoveSource(ChocolateyConfiguration configuration)
             else
             {
                 if (!configuration.QuietOutput) this.Log().Warn(NoChangeMessage);
+
+                if (configuration.Features.UseEnhancedExitCodes && Environment.ExitCode == 0)
+                {
+                    Environment.ExitCode = 2;
+                }
             }
         }
 
@@ -198,6 +208,11 @@ public void DisableSource(ChocolateyConfiguration configuration)
             else
             {
                 if (!configuration.QuietOutput) this.Log().Warn(NoChangeMessage);
+
+                if (configuration.Features.UseEnhancedExitCodes && Environment.ExitCode == 0)
+                {
+                    Environment.ExitCode = 2;
+                }
             }
         }
 
@@ -213,6 +228,11 @@ public void EnableSource(ChocolateyConfiguration configuration)
             else
             {
                 if (!configuration.QuietOutput) this.Log().Warn(NoChangeMessage);
+
+                if (configuration.Features.UseEnhancedExitCodes && Environment.ExitCode == 0)
+                {
+                    Environment.ExitCode = 2;
+                }
             }
         }