Compile issues on old GCC

Hi,

I've modified compile error on old gcc (I'm using gcc 4.4.5).And some test codes run successfully with this branch of OpenNI2.

And I added patch4sse2.This changes the default version of sse. I could not find how to change sse version in command line option, so I made this patch. If there is more smart way to use sse2, please add some notes in OpenNI site.

Thanks