Correct some 2.6 bugs in chained compare ...

and other bugs

* main.py: was botching a version triple test
* parse2{5,6}.py: Add 2.6 try/except end position checking via COME_FROM offsets
* parse26.py: adjust grammar rule for chained-compare2

such as in try-except

uncompyle6/main.py

@@ -315,7 +315,7 @@ def main(
                 else:
                     buffering = 0
                 sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', buffering)
-                if PYTHON_VERSION_TRIPLE > (2, 6):
+                if PYTHON_VERSION_TRIPLE >= (2, 7):
                     tee = subprocess.Popen(["tee", current_outfile],
                                            stdin=subprocess.PIPE)
                     os.dup2(tee.stdin.fileno(), sys.stdout.fileno())