Make JSqueeze filter work with 1.x and 2.x (namespaced)

Also disables the global var renaming behaviour by default
for both 1.x and 2.x (this seems like the safest choice) but
allows setSpecialVarRx(true) to enable it with the default
regex.

src/Assetic/Filter/JSqueezeFilter.php

@@ -23,7 +23,21 @@ class JSqueezeFilter implements FilterInterface
 {
     private $singleLine = true;
     private $keepImportantComments = true;
-    private $specialVarRx = \JSqueeze::SPECIAL_VAR_RX;
+    private $className;
+    private $specialVarRx = false;
+    private $defaultRx;
+
+    function __construct() {
+        // JSqueeze is namespaced since 2.x, this works with both 1.x and 2.x
+        // Upstream default for special var is false in 2.x
+        if (class_exists('\\Patchwork\\JSqueeze')) {
+            $this->className = '\\Patchwork\\JSqueeze';
+            $this->defaultRx = \Patchwork\JSqueeze::SPECIAL_VAR_PACKER;
+        } else {
+            $this->className = '\\JSqueeze';
+            $this->defaultRx = \JSqueeze::SPECIAL_VAR_RX;
+        }
+    }
 
     public function setSingleLine($bool)
     {
@@ -32,7 +46,11 @@ public function setSingleLine($bool)
 
     public function setSpecialVarRx($specialVarRx)
     {
-        $this->specialVarRx = $specialVarRx;
+        if (true === $specialVarRx) {
+            $this->specialVarRx = $this->defaultRx;
+        } else {
+            $this->specialVarRx = $specialVarRx;
+        }
     }
 
     public function keepImportantComments($bool)
@@ -46,7 +64,7 @@ public function filterLoad(AssetInterface $asset)
 
     public function filterDump(AssetInterface $asset)
     {
-        $parser = new \JSqueeze();
+        $parser = new $this->className();
         $asset->setContent($parser->squeeze(
             $asset->getContent(),
             $this->singleLine,