loadBefore(): This forgot to acquire the lock. That's a clear bug.

However, fixing it so far *appears* to fix a bunch of shy FileStorage
pack[Now]WhileWriting test failures whose connection to loadBefore()
isn't obvious.  It's plausible that it's a real fix for those, just
not (yet) compelling.  It seems very likely to be a real fix for very
rare failures that have shown up only in ChrisM's overnight testrunner
reports (because those did have stuff related to loadBefore() in their
tracebacks).

src/ZODB/FileStorage/FileStorage.py

@@ -13,7 +13,7 @@
 ##############################################################################
 """Storage implementation using a log written to a single file.
 
-$Revision: 1.4 $
+$Revision: 1.5 $
 """
 
 import base64
@@ -589,6 +589,8 @@ class FileStorage(BaseStorage.BaseStorage,
             self._lock_release()
 
     def loadBefore(self, oid, tid):
+        self._lock_acquire()
+        try:
             pos = self._lookup_pos(oid)
             end_tid = None
             while True:
@@ -619,6 +621,9 @@ class FileStorage(BaseStorage.BaseStorage,
             else:
                 return self._file.read(h.plen), h.tid, end_tid
 
+        finally:
+            self._lock_release()
+
     def modifiedInVersion(self, oid):
         self._lock_acquire()
         try: