bisect_build: Restore Python 2.5 compatibility.

tools/bisect-builds.py

Index: tools/bisect-builds.py
diff --git a/tools/bisect-builds.py b/tools/bisect-builds.py
index 02ce053dba0202d7910137dd663f1d94b7b5f3d7..e09198f8618be9456668a6dd42ea7fd8711761cd 100755
--- a/tools/bisect-builds.py
+++ b/tools/bisect-builds.py
@@ -211,9 +211,9 @@ def FetchRevision(context, rev, filename, quit_event=None, progress_event=None):
                     displayed.
   """
   def ReportHook(blocknum, blocksize, totalsize):
-    if quit_event and quit_event.is_set():
+    if quit_event and quit_event.isSet():
      raise RuntimeError("Aborting download of revision %d" % rev)
-    if progress_event and progress_event.is_set():
+    if progress_event and progress_event.isSet():
       size = blocknum * blocksize
       if totalsize == -1:  # Total size not known.
         progress = "Received %d bytes" % size
@@ -228,7 +228,7 @@ def FetchRevision(context, rev, filename, quit_event=None, progress_event=None):
   download_url = context.GetDownloadURL(rev)
   try:
     urllib.urlretrieve(download_url, filename, ReportHook)
-    if progress_event and progress_event.is_set():
+    if progress_event and progress_event.isSet():
       print()
   except RuntimeError, e:
     pass