Welcome to the low-tech mini-homework, RecitationHW1.

Here are some functions you'll probably need:

   pickAFolder() - brings up a window to let the user select a folder
   and then returns a string representing the location of that
   folder in the file system.

   os.listdir(folderpath) - returns an array listing all the files and
  folders in the folder given by the folderpath.  The array returned
   is in alphabetical order.

   loadPicture(filepath) - returns a picture object containing the
   picture present at the given filepath.

   wait(numberOfSeconds) - makes the computer wait the given number of
  seconds before executing the next command

So here's the assignment: write a function called playMovie, which
should take no parameters.  The function should have the user pick a
folder containing jpeg pictures which will be played as a movie in
alphabetical order.  The function should then proceed to show all the
pictures (files ending in ".jpg") in the folder with a .15 second
delay between pictures. If no files in the chosen folder are JPEGs, the
function should print "No source video" and terminate.

This assignment is worth 40 homework points. You get 40 points when
you demonstrate the working code to your TA.