(GH-958) If SSLv3 in Posh v2 Fails, Use Original

When original protocol fails in PowerShell v2, `Get-ChocolateyWebFile`
will switch to try the older SSL v3 protocol. When that also fails, the
original protocol should be reinstated.

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

@@ -295,11 +295,13 @@ param(
       if ($host.Version -lt (new-object 'Version' 3,0)) {
         Write-Debug "Converting Security Protocol to SSL3 only for Powershell v2"
         # this should last for the entire duration
+        $originalProtocol = [System.Net.ServicePointManager]::SecurityProtocol
         [System.Net.ServicePointManager]::SecurityProtocol = [System.Net.SecurityProtocolType]::Ssl3
         try {
           $headers = Get-WebHeaders $url -ErrorAction "Stop"
         } catch {
           Write-Host "Attempt to get headers for $url failed.`n  $($_.Exception.Message)"
+          [System.Net.ServicePointManager]::SecurityProtocol = $originalProtocol
         }
       } else {
         Write-Host "Attempt to get headers for $url failed.`n  $($_.Exception.Message)"