#2367 export from slice window ignores options

[Jeremy Faden]

George pointed out that the horizontal slice's export data button ignores the extra options specified in the URI. The URI sent to the formatter should contain the arguments following the question mark, but does not: /foo/blah/file.txt?tformat=microseconds

I made a quick change earlier thinking it was resolving the problem, but this makes it so that the filename cannot be changed. It was a little challenging finding the code to do this properly, and there was a strange chunk where it wasn't clear what it was doing, and I think it's necessary.

Also, the last options used should be kept as well, because presumably the operation will be repeated many times.

[Jeremy Faden]

This is done and will be available in the next devel release.