rust: error for WdirUnsupported with cpython conversion as exception
This introduces WorkingDirectoryUnsupported as an enum variant
of GraphError in the core and converts it to the expected
`mercurial.error.WdirUnsupported`.
#require test-repo jshint hg10
$ . "$TESTDIR/helpers-testrepo.sh"
run jshint on all tracked files ending in .js except vendored dependencies
$ cd "`dirname "$TESTDIR"`"
$ testrepohg locate 'set:**.js' \
> 2>/dev/null \
> | xargs jshint