on windows it is possible to allow a user to list a directory, and at the same 
time disallow opening a file in this directory for reading.

it "hg adds" such a file without trouble, but bails out when doing a "hg 
commit". it would be much nicer to print a warning / question which allows to 
continue the commit anyway.

leaving non-readable files out of a commit would be a possibility also, but i 
guess it slows it down unecessarily.