resolve and shelve ignore the --directory option when file parameters are provided

[Vincent Ladeuil]

This has been introduced as part of revno 5284.

The idea is that the tree should be deduced from the first provided path if --directory is not used and it then ensures that all files are part of the same tree.

Since open_containing(directory) is used in all other cases, the least surprising for the user should be to just do that when both files and --directory are used.