ARRAY enhancements

#1
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
commands).

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

There ought to be a conditional expression
ISARRAY array
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.
--
Steve