Fix package locking on SLE10

SLE10 has python 2.4 installed which is missing the `delete` parameter
from `tempfile.NamedTemporaryFile` (it has been introduced by python 2.6).
This causes the lock code to fail on SLE10.
Merge pull request #18 from flavio/fix_package_locking_on_sle10

Fix package locking on SLE10
changes 0.9.7