Description of problem:
Sometimes pup throws an unhandled exception.

Version-Release number of selected component (if applicable):
pirut-1.2.8-1.fc6

How reproducible:
Sometimes.

Steps to Reproduce:
1. Launch pup.
2.
3.
  
Actual results:
Component: Software Updater
Summary: TB0d6d4bb3 __init__.py:774:downloadHeader:RepoError: failure:
kernel-devel-2.6.22.4-45.fc6.i686.rpm from updates: [Errno 256] No more mirrors
to try.

Traceback (most recent call last):
  File "/usr/sbin/pup", line 433, in _apply
    self.applyChanges(self.mainwin)
  File "/usr/lib/python2.4/site-packages/pirut/__init__.py", line 559, in
applyChanges
    self.checkDeps(mainwin)
  File "/usr/lib/python2.4/site-packages/pirut/__init__.py", line 324, in checkDeps
    self.populateTs(keepold=0)
  File "/usr/lib/python2.4/site-packages/yum/depsolve.py", line 150, in populateTs
    self.downloadHeader(txmbr.po)
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 774, in
downloadHeader
    raise Errors.RepoError, saved_repo_error
RepoError: failure: kernel-devel-2.6.22.4-45.fc6.i686.rpm from updates: [Errno
256] No more mirrors to try.

Local variables in innermost frame:
errors: {}
e: [Errno 2] No such file or directory:
'//var/cache/yum/updates/headers/kernel-devel-2.6.22.4-45.fc6.i686.hdr'
self: <__main__.PackageUpdater object at 0x94e5a6c>
saved_repo_error: failure: kernel-devel-2.6.22.4-45.fc6.i686.rpm from updates:
[Errno 256] No more mirrors to try.
repo: updates
checkfunc: (<bound method PackageUpdater.verifyHeader of
<__main__.PackageUpdater object at 0x94e5a6c>>,
(<yum.sqlitesack.YumAvailablePackageSqlite object at 0xb10f6cc>, 1), {})
local: //var/cache/yum/updates/headers/kernel-devel-2.6.22.4-45.fc6.i686.hdr
po: kernel-devel - 2.6.22.4-45.fc6.i686

Expected results:
Should either work, or inform the user that the files are not available yet.

Additional info:
This problem will probably go away.  It happens on some updates when the update
is first released, and will go away in about 24 hours (assuming this is the
problem I've had many times before).