Description of problem:
Mock on el6 can't build against rawhide (can everything else):

$ mock -r fedora-rawhide-x86_64 --no-cleanup-after /local/home/rpmb/rpmbuild/SRPMS/gerris-1.3.2-3.20111123.el6.src.rpm
INFO: mock.py version 1.1.18 starting...
State Changed: init plugins
INFO: selinux enabled
WARNING: selinux: 'yum' does not support '--setopt' option
State Changed: start
INFO: Start(/local/home/rpmb/rpmbuild/SRPMS/gerris-1.3.2-3.20111123.el6.src.rpm)  Config(fedora-rawhide-x86_64)
State Changed: lock buildroot
State Changed: clean
INFO: chroot (/var/lib/mock/fedora-rawhide-x86_64) unlocked and deleted
State Changed: unlock buildroot
State Changed: init
State Changed: lock buildroot
Mock Version: 1.1.18
INFO: Mock Version: 1.1.18
INFO: calling preinit hooks
INFO: enabled root cache
INFO: enabled yum cache
State Changed: cleaning yum metadata
INFO: enabled ccache
State Changed: running yum
ERROR: Exception(/local/home/rpmb/rpmbuild/SRPMS/gerris-1.3.2-3.20111123.el6.src.rpm) Config(fedora-rawhide-x86_64) 0 minutes 4 seconds
INFO: Results and/or logs in: /var/lib/mock/fedora-rawhide-x86_64/result
ERROR: Command failed: 
 # ['/usr/bin/yum', '--installroot', '/var/lib/mock/fedora-rawhide-x86_64/root/', 'groupinstall', 'buildsys-build']
Traceback (most recent call last):
  File "/usr/bin/yum", line 29, in <module>
    yummain.user_main(sys.argv[1:], exit_code=True)
  File "/usr/share/yum-cli/yummain.py", line 254, in user_main
    errcode = main(args)
  File "/usr/share/yum-cli/yummain.py", line 109, in main
    result, resultmsgs = base.doCommands()
  File "/usr/share/yum-cli/cli.py", line 353, in doCommands
    self._getTs(needTsRemove)
  File "/usr/lib/python2.6/site-packages/yum/depsolve.py", line 99, in _getTs
    self._getTsInfo(remove_only)
  File "/usr/lib/python2.6/site-packages/yum/depsolve.py", line 110, in _getTsInfo
    pkgSack = self.pkgSack
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 774, in <lambda>
    pkgSack = property(fget=lambda self: self._getSacks(),
  File "/usr/lib/python2.6/site-packages/yum/__init__.py", line 564, in _getSacks
    self.repos.populateSack(which=repos)
  File "/usr/lib/python2.6/site-packages/yum/repos.py", line 279, in populateSack
    sack.populate(repo, mdtype, callback, cacheonly)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 164, in populate
    if self._check_db_version(repo, mydbtype):
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 223, in _check_db_version
    return repo._check_db_version(mdtype)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1227, in _check_db_version
    repoXML = self.repoXML
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1427, in <lambda>
    repoXML = property(fget=lambda self: self._getRepoXML(),
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1419, in _getRepoXML
    self._loadRepoXML(text=self)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1409, in _loadRepoXML
    return self._groupLoadRepoXML(text, self._mdpolicy2mdtypes())
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1385, in _groupLoadRepoXML
    self._commonRetrieveDataMD(mdtypes)
  File "/usr/lib/python2.6/site-packages/yum/yumRepo.py", line 1369, in _commonRetrieveDataMD
    misc.bunzipFile(dl_local, local)
  File "/usr/lib/python2.6/site-packages/yum/misc.py", line 687, in bunzipFile
    data = s_fn.read(1024000)
EOFError: compressed file ended before the logical end-of-stream was detected


Version-Release number of selected component (if applicable):
mock-1.1.18-1.el6.noarch