rust-cpython: raising error.WdirUnsupported
The Graph implementation of hg-cpython returns the appropriate error
upon encounter with the working directory special revision number, and
this gives us in particular a code path to test from test-rust-ancestors.py
In the current implementation, the exception is actually raised from
the iterator instantiation; we are nonetheless consuming the iterator
in the test with `list()` in order not to depend on implementation details.
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present