ARRAY enhancements

It would be useful to have an enhanced version of the commands which load
data into arrays to include defintion of the arrays of "just the right
size", e.g.

echo %@makefilearray[array,file]

would be equivalent to:

unsetarray array
setarray array[%@lines[file]]
echo %@filearray[array,file]

and similar functionality for @EXECARRAY (which is harder to emulate with

@EXECARRAY should return the number of array elements it filled in the same
manner as @FILEARRAY does.

There ought to be a conditional expression
which would allow simpler testing for existence of arrays then the hard to
understand but available
%@arrayinfo[array] NE -1

BTW, all but ISARRAY could be implemented via plugins.