I know which test is failing ... I just failed myself to check in the fix :-}
Beside of that, Silva should run fine without PIL.
Seemingly only a few people are running this w/o PIL.
[Maybe someone should setup a test zoo with lots of test installations
with various combinations of Zope versions / Extension products ...
hm, maybe should I do this ;-)]
What other tests are failing for You without ExtFile?
I do not have ExtFile installed, and the only test failing for me is
the test_manage_convertStorage (Silva.tests.test_fileservices.FileServicesTest)