Forward port from Zope 2.7 branch.

oid_repr():  Make it obvious which base is intended.  The output was
3-way ambiguous.

NEWS.txt

+What's new in ZODB3 3.3 ?
+=========================
+Release date: DD-MMM-YYYY
+
+Tools
+--------
+
+ZODB.utils.oid_repr() changed to add a leading "0x", and to strip leading
+zeroes.  This is used, e.g., in the detail of a POSKeyError exception, to
+identify the missing oid.  Before, the output was ambiguous.  For example,
+oid 17 was displayed as 0000000000000011.  As a Python integer, that's
+octal 9.  Or was it meant to be decimal 11?  Or was it meant to be hex?
+Now it displays as 0x11.
+
+
 What's new in ZODB3 3.3 beta 2
 ==============================
 Release date: 13-Aug-2004

src/ZODB/tests/testmvcc.py

@@ -145,7 +145,7 @@ commit the transaction.
 >>> tm2.get().commit()
 Traceback (most recent call last):
  ...
-ConflictError: database conflict error (oid 0000000000000001, class ZODB.tests.MinPO.MinPO)
+ConflictError: database conflict error (oid 0x01, class ZODB.tests.MinPO.MinPO)
 
 The failed commit aborted the current transaction, so we can try
 again.  This example will demonstrate that we can commit a transaction
@@ -338,7 +338,7 @@ False
 >>> r1["b"]._p_activate()
 Traceback (most recent call last):
  ...
-ReadConflictError: database read conflict error (oid 0000000000000002, class ZODB.tests.MinPO.MinPO)
+ReadConflictError: database read conflict error (oid 0x02, class ZODB.tests.MinPO.MinPO)
 >>> oid in cn1._invalidated
 True
 >>> ts.count

src/ZODB/utils.py

@@ -14,10 +14,11 @@
 
 import sys
 import time
-from persistent.TimeStamp import TimeStamp
-
 from struct import pack, unpack
 from types import StringType
+from binascii import hexlify
+
+from persistent.TimeStamp import TimeStamp
 
 z64 = '\0'*8
 t32 = 1L << 32
@@ -64,7 +65,14 @@ def newTimeStamp(old=None,
 
 def oid_repr(oid):
     if isinstance(oid, StringType) and len(oid) == 8:
-        return '%016x' % U64(oid)
+        # Convert to hex and strip leading zeroes.
+        as_hex = hexlify(oid).lstrip('0')
+        # Ensure two characters per input byte.
+        if len(as_hex) & 1:
+            as_hex = '0' + as_hex
+        elif as_hex == '':
+            as_hex = '00'
+        return '0x' + as_hex
     else:
         return repr(oid)