(chocolatey#1760) config exit 2 if nothing to do

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

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

@@ -128,12 +128,17 @@ 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, config already set/unset (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, "See It In Action");
             "chocolatey".Log().Info(@"

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

@@ -441,6 +441,11 @@ public void config_set(ChocolateyConfiguration configuration)
                 if (configuration.ConfigCommand.ConfigValue.is_equal_to(currentValue.to_string()))
                 {
                     this.Log().Warn(NO_CHANGE_MESSAGE);
+
+                    if (configuration.Features.UseEnhancedExitCodes && Environment.ExitCode == 0)
+                    {
+                        Environment.ExitCode = 2;
+                    }
                 }
                 else
                 {
@@ -458,6 +463,11 @@ public void config_unset(ChocolateyConfiguration configuration)
             if (config == null || string.IsNullOrEmpty(config.Value))
             {
                 this.Log().Warn(NO_CHANGE_MESSAGE);
+
+                if (configuration.Features.UseEnhancedExitCodes && Environment.ExitCode == 0)
+                {
+                    Environment.ExitCode = 2;
+                }
             }
             else
             {