transaction: windows workaround for missing line iteration support

The mixedfilemodewrapper doesn't support line iteration, so just read
the whole file in one go.

Differential Revision: https://phab.mercurial-scm.org/D9532

mercurial/transaction.py

@@ -418,7 +418,7 b' class transaction(util.transactional):'
     def readjournal(self):
         self._file.seek(0)
         entries = []
-        for l in self._file:
+        for l in self._file.readlines():
             file, troffset = l.split(b'\0')
             entries.append((file, int(troffset)))
         return entries