[PATCH] Check case-folding clashes during addremove

[Andrei Vermel]

> This really should go into dirstate.py, so that hg add can also benefit
> from it.  If you look at the dirstate.update function, you'll see that
> we already do some checks when state == 'a' (i.e. we're adding a file).

There's a small problem with this. Although dirstate.update() takes 'files',
turns out it is called for each file separately. Rebuilding the name clash
map for each added file would be an overhead for big number of added
files.
As an option, the clash map can persist in dirstate and get updated
incrementally with dirstate.map. What do you think?

Andrei