#19 trace message box problem

[Alex Forencich]

When trace mode is selected and the only active
equation is cleared, a box entitled "Equation Error"
with the text

ERROR: Please enter an equation first
EQUATION ENTERED:

appears. When the OK button is clicked, the box pops
up again. This repeats until the cursor is moved off
the graph window and trace is disabled. Reccommended
fix: automatically disable trace if this error occurs.
This will alleviate frustration of the end user
because the box will only pop up once.