Fix Flash and JavaApplet object XML rendering.

Hi y'all, thanks for the fantastic library.

This is regarding the issue here:
https://github.com/boto/boto/issues/203

The Flash and JavaApplet objects fail to render XML properly because content variable is reinitialized when get_inner_content() is called. This is just @haltil's fix implemented. I needed to be able to pip install a fixed version from a repo, and thought I'd send this upstream. Tested and working for Flash objects.

Cheers,
Yuri