STOPLOOP - creates stop button to have a user interrupt a loop

FS = STOPLOOP creates a message box window and returns a structure FS that
holds two functions, called FS.Stop and FS.Clear. The function FS.Stop()
will return true, if the OK button has been clicked (or the message box
has been removed), so that a loop can be interrupted.

The function FS.Clear() can be used to remove the message box, if a loop has ended without user interruption.

FS = STOPLOOP(STR) uses the string STR to display instead of the default
'Stop the Loop'.

Example:
tic ; % We will measure elapsed time in a loop
% Set up the stop box:
FS = stoploop({'Stop me before', '5 seconds have elapsed'}) ;
% Display elapsed time
fprintf('\nSTOPLOOP: elapsed time (s): %5.2f\n',toc)
% start the loop
while(~FS.Stop() && toc < 5), % Check if the loop has to be stopped
fprintf('%c',repmat(8,6,1)) ; % clear up previous time
fprintf('%5.2f\n',toc) ; % display elapsed time
end
FS.Clear() ; % Clear up the box
clear FS ; % this structure has no use anymore

Version 1.0, jun 2008
Inspired by several posts on the FEX on "how to interrupt a loop?".