(GH-676) Fix: Unzip specific folder feature is broken

Previously, when attempting to unzip a subdirectory in a zipped
archive, the Chocolatey unzip functions were ignoring the `SpecificFolder`
parameter. This was caused by a change to use 7za.exe in August 2013 in commit
chocolatey-archive/chocolatey@2e83d2e.

That changed carried over into the newer codebase. More recently there was a
switch back to 7z.exe (full 7zip), so it is possible to unzip a subdirectory
in an archive again. Ensure that `SpecficFolder` is added to the 7zip options
when it is specified.

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

@@ -80,9 +80,6 @@ param(
   [parameter(ValueFromRemainingArguments = $true)][Object[]] $ignoredArguments
 )
   $zipfileFullPath=$fileFullPath
-  if ($specificfolder) {
-    $fileFullPath=join-path $fileFullPath $specificFolder
-  }
 
   Write-FunctionCallLogMessage -Invocation $MyInvocation -Parameters $PSBoundParameters
 
@@ -123,6 +120,9 @@ param(
   }
 
   $params = "x -aoa -bd -bb1 -o`"$destinationNoRedirection`" -y `"$fileFullPathNoRedirection`""
+  if ($specificfolder) {
+    $params += " `"$specificfolder`""
+  }
   Write-Debug "Executing command ['$7zip' $params]"
 
   # Capture 7z's output into a StringBuilder and write it out in blocks, to improve I/O performance.