(GH-603) Fix - Get-FileName errors sometimes

When running Get-FileName, if HttpWebResponse is not fully qualified,
PowerShell 5 will not know how to find it. It's better to fully qualify
classes, so fix that to be correct.

Also pass along the actual error when it occurs.

src/chocolatey.resources/helpers/functions/Get-FileName.ps1

@@ -85,7 +85,7 @@ param(
 
   try
   {
-    [HttpWebResponse]$response = $request.GetResponse()
+    [System.Net.HttpWebResponse]$response = $request.GetResponse()
     if ($response -eq $null) { 
       $response.Close() 
       return $originalFileName 
@@ -134,7 +134,7 @@ param(
   {
     $request.ServicePoint.MaxIdleTime = 0
     $request.Abort();
-    Write-Debug "Url request/response failed - file name will be '$originalFileName'"
+    Write-Debug "Url request/response failed - file name will be '$originalFileName':  $($_)"
 
     return $originalFileName
   }