subrepo: handle missing subrepo spec file as removed
Otherwise, all commands involving a dirstate walk will abort when trying to
readone of them. Deleting .hgsub basically breaks a repository.
$ hg init repo
$ cd repo
$ hg init subrepo
$ echo a > subrepo/a
$ hg -R subrepo ci -Am adda
adding a
$ echo 'subrepo = subrepo' > .hgsub
$ hg ci -Am addsubrepo
adding .hgsub
committing subrepository subrepo
$ echo b > subrepo/b
$ hg -R subrepo ci -Am addb
adding b
$ hg ci -m updatedsub
committing subrepository subrepo
delete .hgsub and revert it
$ rm .hgsub
$ hg revert .hgsub
warning: subrepo spec file .hgsub not found
delete .hgsubstate and revert it
$ rm .hgsubstate
$ hg revert .hgsubstate
delete .hgsub and update
$ rm .hgsub
$ hg up 0
warning: subrepo spec file .hgsub not found
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg st
! .hgsub
$ ls subrepo
a
delete .hgsubstate and update
$ hg up -C
warning: subrepo spec file .hgsub not found
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ rm .hgsubstate
$ hg up 0
remote changed .hgsubstate which local deleted
use (c)hanged version or leave (d)eleted? c
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg st
$ ls subrepo
a