manifest: improve error message in case for tree manifest
In the case where tree manifest is not enabled but we still receive an sub
directory information for the manifest. The error now inform which sub-directory
was passed.
$ cat >> $HGRCPATH <<EOF
> [censor]
> policy=ignore
> EOF
$ mkdir r
$ cd r
$ hg init
$ echo secret > target
$ hg commit -Am "secret"
adding target
$ touch bystander
$ hg commit -Am "innocent"
adding bystander
$ echo erased-secret > target
$ hg commit -m "erased secret"
$ hg censor target --config extensions.censor= -r ".^^"
$ hg update ".^"
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cat target
$ hg update tip
1 files updated, 0 files merged, 0 files removed, 0 files unresolved