simplify the loop in Node.listchain

CHANGELOG

@@ -29,6 +29,7 @@ Changes between 2.1.3 and 2.2.0
 - fix issue83: link to generated funcarg list
 - fix issue74: pyarg module names are now checked against imp.find_module false positives
 - fix compatibility with twisted/trial-11.1.0 use cases
+- simplify Node.listchain
 
 Changes between 2.1.2 and 2.1.3
 ----------------------------------------

_pytest/main.py

@@ -229,13 +229,13 @@ class Node(object):
     def listchain(self):
         """ return list of all parent collectors up to self,
             starting from root of collection tree. """
-        l = [self]
+        chain = []
-        while 1:
+        item = self
-            x = l[0]
+        while item is not None:
-            if x.parent is not None: # and x.parent.parent is not None:
+            chain.append(item)
-                l.insert(0, x.parent)
+            item = item.parent
-            else:
+        chain.reverse()
-                return l
+        return chain
 
     def listnames(self):
         return [x.name for x in self.listchain()]