dirstate._dirs: fix refcounting broken by 7dfac37cfabf
reported by Patrick Waugh
adding bar
adding foo
adding quux1
adding quux2
created new head
merging bar
merging bar failed!
merging foo and baz to baz
1 files updated, 1 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges
U bar
R baz
3 files updated, 0 files merged, 1 files removed, 0 files unresolved
merging bar
merging bar failed!
merging baz and foo to baz
1 files updated, 1 files merged, 0 files removed, 1 files unresolved
use 'hg resolve' to retry unresolved file merges
% show unresolved
U bar
R baz
% unmark baz
% show
U bar
U baz
% re-resolve baz
merging baz and foo to baz
% after
U bar
R baz
% resolve all
merging bar
warning: conflicts during merge.
merging bar failed!
% after
U bar
R baz