hgweb: handle exception of misconfigured path on index page
If hgweb.config contains wrong path mapping, hgweb causes internal server
error on repository index page.
This patch changes makeindex() to ignore RepoError, because it looks to be
designed to suppress configuration error.
% file replaced with directory
adding a
% should fail - would corrupt dirstate
abort: file 'a' in dirstate clashes with 'a/a'
% directory replaced with file
adding a/a
% should fail - would corrupt dirstate
abort: directory 'a' already in dirstate
% directory replaced with file
adding b/c/d
% should fail - would corrupt dirstate
abort: directory 'b' already in dirstate