--- a/mercurial/transaction.py	Sat May 29 20:32:39 2010 +0200
+++ b/mercurial/transaction.py	Thu May 27 17:47:40 2010 +0200
@@ -43,6 +43,7 @@
 class transaction(object):
     def __init__(self, report, opener, journal, after=None, createmode=None):
         self.count = 1
+        self.usages = 1
         self.report = report
         self.opener = opener
         self.after = after
@@ -108,8 +109,16 @@
     @active
     def nest(self):
         self.count += 1
+        self.usages += 1
         return self
 
+    def release(self):
+        if self.count > 0:
+            self.usages -= 1
+        # of the transaction scopes are left without being closed, fail
+        if self.count > 0 and self.usages == 0:
+            self._abort()
+
     def running(self):
         return self.count > 0
 
@@ -136,6 +145,7 @@
 
     def _abort(self):
         self.count = 0
+        self.usages = 0
         self.file.close()
 
         try: