IE7 slowdown

[bill]

Run benchTool.html to create 1000 button widgets, then reload the page, the run again, the reload the page, etc. Originally takes 6.5s but then each time goes up 1s or 2s. Happens even on IE7.

[guest]

Part of this is probably due to the memory leak that still seems to exist on IE7. ​http://trac.dojotoolkit.org/ticket/3531#comment:14 Even creating 100 button widgets and reloading leaks 301 elements each time you reload.

[bill]

(In [10043]) Fixes #4046: cleanup code is necessary for IE7 too

[bill]

Note: cleanup code was removed completely in [28551]. It didn't seem to be needed for memory leaks. I didn't test browser performance though, although not sure if we care about that for IE7 since it's fast becoming obsolete.