Allow command line "!" bang operator to be fed from more than just the local variable named %

There are times when it is useful to have the command line "!" (bang) get its input from more than just the single local variable named "%". Currently, the code retrieves sequential integers as the first subscript of the % lvn.

I propose that there be a method (probably a VIEW command) that changes the source of data for this command line operator. I would like to see it supporting sequential subscripts from a global variable, or calling a $$entryref when given the next sequential value as an input.

This is an issue to remind me (and possibly John Willis) that this might be interesting to work on.