Fix Jira Bug I7-2460

[neroden]

https://inform7.atlassian.net/jira/software/c/projects/I7/issues/I7-2460?filter=updatedrecently

This allows the sensible error messages from "remove" to trigger rather than giving strange "you can't see any such thing" errors.

[neroden]

The first version of this didn't work right and broke a bunch of stuff, due to some important things I overlooked when trying to convert it from an extension to a patch (which is an error-prone process).

The new version doesn't break anything. It fixes the error message for the single-item case ("REMOVE CAT FROM BOX" where the cat is in the room but not in the box), which is by far the most common case, and at least means that the error message in Standard Rules gets printed sometimes (rather than never ever being used, which is the situation without any patch).

The multi-item case ("REMOVE CAT AND DOG FROM BOX") is too hairy to handle at this time and still gives "You can't see any such thing". This is largely due to the amount of special casing of ##Remove in the I6 parser, and the inaccessibility of the look-forward code to any token other than multiinside and multiexcept. (I may approach it again after I've figured out how to make the look-forward code accessible to the "deciding whether all includes" activity.)