(chocolateyGH-603) Get-FileName should set proxy if required

As the other two web calls check/use proxy and network credentials,
Get-FileName should also use a proxy if required.

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

@@ -31,6 +31,47 @@ param(
     return $originalFileName 
   }
 
+  $defaultCreds = [System.Net.CredentialCache]::DefaultCredentials
+  if ($defaultCreds -ne $null) {
+    $request.Credentials = $defaultCreds
+  }
+
+  $client = New-Object System.Net.WebClient
+  if ($defaultCreds -ne $null) {
+    $client.Credentials = $defaultCreds
+  }
+
+  # check if a proxy is required
+  $explicitProxy = $env:chocolateyProxyLocation
+  $explicitProxyUser = $env:chocolateyProxyUser
+  $explicitProxyPassword = $env:chocolateyProxyPassword
+  if ($explicitProxy -ne $null) {
+    # explicit proxy
+    $proxy = New-Object System.Net.WebProxy($explicitProxy, $true)
+    if ($explicitProxyPassword -ne $null) {
+    $passwd = ConvertTo-SecureString $explicitProxyPassword -AsPlainText -Force
+    $proxy.Credentials = New-Object System.Management.Automation.PSCredential ($explicitProxyUser, $passwd)
+  }
+
+    Write-Debug "Using explicit proxy server '$explicitProxy'."
+    $request.Proxy = $proxy
+
+  } elseif (!$client.Proxy.IsBypassed($url))
+  {
+    # system proxy (pass through)
+    $creds = [Net.CredentialCache]::DefaultCredentials
+    if ($creds -eq $null) {
+      Write-Debug "Default credentials were null. Attempting backup method"
+      $cred = Get-Credential
+      $creds = $cred.GetNetworkCredential();
+    }
+    $proxyAddress = $client.Proxy.GetProxy($url).Authority
+    Write-Debug "Using system proxy server '$proxyaddress'."
+    $proxy = New-Object System.Net.WebProxy($proxyAddress)
+    $proxy.Credentials = $creds
+    $request.Proxy = $proxy
+  }
+
   $request.Method = "GET"
   $request.Accept = '*/*'
   $request.AllowAutoRedirect = $true