Handle LC_NUMERIC with comma decimal separator

Closes #399.

lib/PhpParser/PrettyPrinter/Standard.php

@@ -182,6 +182,11 @@ class Standard extends PrettyPrinterAbstract
             $stringValue = sprintf('%.17G', $node->value);
         }
 
+        // %G is locale dependent and there exists no locale-independent alternative. We don't want
+        // mess with switching locales here, so let's assume that a comma is the only non-standard
+        // decimal separator we may encounter...
+        $stringValue = str_replace(',', '.', $stringValue);
+
         // ensure that number is really printed as float
         return preg_match('/^-?[0-9]+$/', $stringValue) ? $stringValue . '.0' : $stringValue;
     }