Add additional hooks for subclasses

Fixes #22

Also some minor refactoring with an eye towards speed and simplicity.
We get between 5 and 10% faster, even accounting for all the overhead
of raising exceptions:

+----------------+---------------+------------------------------+
| Benchmark      | masterresults | issue22results               |
+================+===============+==============================+
| trivial commit | 14.9 us       | 13.2 us: 1.12x faster (-11%) |
+----------------+---------------+------------------------------+
| max retries    | 16.0 us       | 15.1 us: 1.06x faster (-5%)  |
+----------------+---------------+------------------------------+

CHANGES.rst

@@ -16,6 +16,12 @@
   retried. Previously, an error there would probably be raised
   *anyway* and not retried, unless a subclass had made customizations.
 
+- Add ``setUp`` and ``tearDown`` methods to TransactionLoop to give
+  subclasses a place to hook into the inners of the transaction loop.
+  This is particularly helpful if they need to do something after the
+  transaction manager has been put in explicit mode. See `issue 22
+  <https://github.com/NextThought/nti.transactions/issues/22>`_.
+
 2.0.1 (2019-09-03)
 ==================
 

src/nti/transactions/tests/test_transaction.py

@@ -40,7 +40,7 @@ class RaisingCommit(object):
         def __init__(self, t=Exception):
             self.t = t
 
-        def commit(self):
+        def nti_commit(self):
             if self.t:
                 raise self.t
 
@@ -186,7 +186,7 @@ def test_note(self, fake_begin, fake_get):
         fake_tx = fudge.Fake()
         (fake_tx
          .expects('note').with_args(u'Hi')
-         .expects('abort')
+         .expects('nti_abort')
          .provides('isDoomed').returns(True))
         fake_begin.expects_call().returns(fake_tx)
         fake_get.expects_call().returns(fake_tx)
@@ -202,7 +202,7 @@ def describe_transaction(self, *args, **kwargs):
                  'transaction._manager.TransactionManager.get')
     def test_abort_no_side_effect(self, fake_begin, fake_get):
         fake_tx = fudge.Fake()
-        fake_tx.expects('abort')
+        fake_tx.expects('nti_abort')
 
         fake_begin.expects_call().returns(fake_tx)
         fake_get.expects_call().returns(fake_tx)
@@ -214,7 +214,7 @@ class Loop(TransactionLoop):
         result = Loop(lambda: 42)()
         assert_that(result, is_(42))
 
-    @fudge.patch('transaction._transaction.Transaction.abort')
+    @fudge.patch('transaction._transaction.Transaction.nti_abort')
     def test_abort_doomed(self, fake_abort):
         fake_abort.expects_call()
 
@@ -230,7 +230,7 @@ def handler():
                  'transaction._manager.TransactionManager.get')
     def test_abort_veto(self, fake_begin, fake_get):
         fake_tx = fudge.Fake()
-        fake_tx.expects('abort')
+        fake_tx.expects('nti_abort')
         fake_tx.provides('isDoomed').returns(False)
 
         fake_begin.expects_call().returns(fake_tx)