This fixes a bug that Chris Mason found. As for a test case, I can't think of one. It's a very weird case. Basically, if there is a file listed as changed in the changelog entry, but not showing up in any of the associated manifest entries, hg would abort when trying to create a changeset. Now it just decides the file must not have any versions relevant to the changeset.

%%% should show a removed and b added
A b
R a
reverting...
%%% should show b unknown and a back to normal
? b
merging a
%%% should show foo-b
foo-b
%%% should show a removed and b added
A b
R a
reverting...
%%% should show b unknown and a marked modified (merged)
? b
%%% should show foo-b
foo-b