Popover with backdrop causes successive popovers not to close.

[vanboom]

Steps to reproduce the issue:

1. create a backdrop popover and a regular popover
2. click the backdrop popover and then close it by clicking outside the area
3. click the regular popover and then try to close it by clicking outside the popover area

The flag _isBodyEventHandled is not getting cleared, causing the body events for the other popovers not to be handled.

Set _isBodyEventHandled = false around line 328 inside the show method to fix this issue.