reported by Georg <gwk.rko@googlemail.com>

testcase:

  509  mkdir remove
  510  cd remove/
  511  hg init
  512  touch a
  513  hg ci -A -m m
  514  hg rm a
  515  hg ci -m m
  516  hg serve

and then browse http://localhost:8000/?cs=1 and click
http://localhost:8000/?f=000000000000;file=a ('a' link in files)

it should show a 'file not found' template instead of a traceback.