adding shutdown() methods to the plot (based on patch by Ryley
Breiddal, issue 269). This prevents a memory leak in Chrome and
hopefully makes replotting faster for those who are using $.plot
instead of .setData()/.draw(). Also update jQuery to 1.5.1 to prevent
IE leaks fixed some time ago in jQuery.


git-svn-id: https://flot.googlecode.com/svn/trunk@317 1e0a6537-2640-0410-bfb7-f154510ff394