Fix performance regression in addremove command.
When I rewrote addremove, I lazily put a call to repo.changes in,
which was unnecessary and slow. This is a new rewrite, preserving the
file name behaviour, but replacing the call to repo.changes with a walk,
which is much cheaper, and avoids calls to os.stat on all but files that
have probably been deleted.
+ mkdir t
+ cd t
+ hg init
+ hg id
unknown
+ echo a
+ hg add a
+ hg commit -m test -d '0 0'
+ hg co
+ hg identify
acb14030fe0a tip
++ hg -q tip
++ cut -d : -f 2
+ T=acb14030fe0a21b60322c440ad2d20cf7685a376
+ echo 'acb14030fe0a21b60322c440ad2d20cf7685a376 first'
+ cat .hgtags
acb14030fe0a21b60322c440ad2d20cf7685a376 first
+ hg add .hgtags
+ hg commit -m 'add tags' -d '0 0'
+ hg tags
tip 1:b9154636be938d3d431e75a7c906504a079bfe07
first 0:acb14030fe0a21b60322c440ad2d20cf7685a376
+ hg identify
b9154636be93 tip
+ echo bb
+ hg status
M a
+ hg identify
b9154636be93+ tip
+ hg co first
+ hg id
acb14030fe0a+ first
+ hg -v id
acb14030fe0a21b60322c440ad2d20cf7685a376+ first
+ hg status
M a
+ echo 1
+ hg add b
+ hg commit -m branch -d '0 0'
+ hg id
c8edf04160c7 tip
+ hg co -m 1
+ hg id
c8edf04160c7+b9154636be93+ tip
+ hg status
M .hgtags
M a