Fix confusing message from hg revert (issue332)
% mkdir sub1
% touch sub1/file1
% hg add sub1/
adding sub1/file1
% hg rev sub1
sub1: No such file in rev e4c586763258
forgetting sub1/file1
#header#<title>Mercurial Error</title></head><body><h2>Mercurial Error</h2><p>An error occured while processing your request:</p><p>#error|escape#</p>#footer#