Add Perl support for ucalls / uflow / ustat (#1959)

Sort language entries while at it.
diff --git a/tests/python/test_utils.py b/tests/python/test_utils.py
index 69dddf6..54b97cf 100755
--- a/tests/python/test_utils.py
+++ b/tests/python/test_utils.py
@@ -15,7 +15,7 @@
         self.assertEqual(len(online_cpus), num_cores)
 
     def test_detect_language(self):
-        candidates = ["java", "ruby", "php", "node", "c", "python"]
+        candidates = ["c", "java", "perl", "php", "node", "ruby", "python"]
         language = detect_language(candidates, os.getpid())
         self.assertEqual(language, "python")