(chocolatey#2078) Skip importing Chocolatey GUI Extension

The Chocolatey GUI Extension is a "special" extension in the sense that
it isn't intended to work with Chocolatey directly, but it is shipped as
a "normal" Chocolatey extension. We don't want to load the
chocolateygui.licensed.dll into the choco.exe process, but rather leave
it alone, and allow Chocolatey GUI to load it when required.

src/chocolatey.resources/helpers/chocolateyInstaller.psm1

@@ -1,4 +1,4 @@
-# Copyright © 2017 Chocolatey Software, Inc.
+# Copyright © 2017 Chocolatey Software, Inc.
 # Copyright © 2015 - 2017 RealDimensions Software, LLC
 # Copyright © 2011 - 2015 RealDimensions Software, LLC & original authors/contributors from https://github.com/chocolatey/chocolatey
 #
@@ -73,7 +73,11 @@ if (Test-Path($extensionsPath)) {
         }
 	    }
 
-	    if (!$loaded) { Import-Module $path; }
+	    if (!$loaded) {
+        if ($fileNameWithoutExtension -ne "chocolateygui.licensed") {
+          Import-Module $path;
+        }
+      }
     } catch {
       if ($env:ChocolateyPowerShellHost -eq 'true') {
         Write-Warning "Import failed for '$path'.  Error: '$_'"