Handle a nonexistent repository with a 404 error.
Based on changeset 62ea868cafbfa3acb7e5dba6982ecb46a1637246 from
Vincent Wagelaar <vincent@ricardis.tudelft.nl>
in http://hannibal.lr-s.tudelft.nl/~vincent/fcgi
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b4d0c3786ad3e47beacf8412157326a32b6d25a4 0.4c
f40273b0ad7b3a6d3012fd37736d0611f41ecf54 0.5
0a28dfe59f8fab54a5118c5be4f40da34a53cdb7 0.5b
12e0fdbc57a0be78f0e817fd1d170a3615cd35da 0.6
4ccf3de52989b14c3d84e1097f59e39a992e00bd 0.6b
eac9c8efcd9bd8244e72fb6821f769f450457a32 0.6c