(chocolateyGH-527) Url is optional

Some packages should be able to support 64 bit only. In those
cases Chocolatey should allow 32 bit urls to be optional
and fail the package on 32 bit systems with a helpful message.

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

@@ -127,7 +127,7 @@ Get-FtpFile
 param(
   [parameter(Mandatory=$true, Position=0)][string] $packageName,
   [parameter(Mandatory=$true, Position=1)][string] $fileFullPath,
-  [parameter(Mandatory=$true, Position=2)][string] $url,
+  [parameter(Mandatory=$false, Position=2)][string] $url = '',
   [parameter(Mandatory=$false, Position=3)][string] $url64bit = '',
   [parameter(Mandatory=$false)][string] $checksum = '',
   [parameter(Mandatory=$false)][string] $checksumType = '',
@@ -172,6 +172,12 @@ param(
     $checksumType = $checksumType32
   }
 
+  # If we're on 32 bit or attempting to force 32 bit and there is no
+  # 32 bit url, we need to throw an error.
+  if ($url -eq $null -or $url -eq '') {
+    throw "This package does not support $bitWidth bit architecture."
+  }
+
   if ($getOriginalFileName) {
     try {
       $fileDirectory = [System.IO.Path]::GetDirectoryName($fileFullPath)

src/chocolatey.resources/helpers/functions/Install-ChocolateyPackage.ps1

@@ -198,7 +198,7 @@ param(
   [parameter(Mandatory=$false, Position=1)]
   [alias("installerType","installType")][string] $fileType = 'exe',
   [parameter(Mandatory=$false, Position=2)][string] $silentArgs = '',
-  [parameter(Mandatory=$false, Position=3)][string] $url,
+  [parameter(Mandatory=$false, Position=3)][string] $url = '',
   [parameter(Mandatory=$false, Position=4)]
   [alias("url64")][string] $url64bit = '',
   [parameter(Mandatory=$false)]$validExitCodes = @(0),