calculate activity outputs the incorrect error message if variable is changed in function

[phoenix14113]

function f(y) { if (arguments.length != 1) { throw new SyntaxError("Wrong number of arguments in function f (" + arguments.length + " provided, 1 expected)"); } return y }

This is output when you change the x in f(x) to any other letter. the correct error message should be "invalid left hand side of assignment operator =".

[phoenix14113]

If you enter any character except x in the f(x) graphing utility for example:

you get this error message inside of the input box:

and if you press enter when this error message is inside the input box you get this:

[llaske]

Fixed in #950