Make JSqueeze filter work with 1.x and 2.x (namespaced)

JSqueeze 2.x just came out, and it's now namespaced. This should let the filter work with both 1.x and 2.x. Obviously it'd also be simple to just make it work with 2.x only if you wanted to go that way.

I thought about adding some helper bits to make it easier to use upstream's default special var regex on 2.x, but thought I'd just keep it simple for now. We could do something like have `setSpecialVarRx` accept 'true', and have that set the value to `JSqueeze::SPECIAL_VAR_PACKER` on 2.x.

@nicolas-grekas wdyt?

It'd be good to have this on the stable branches too.
It actually does work, yeah - i was a bit surprised too, but the unit tests do actually check this (I know because I got it wrong about ten times first, hence the "yakity sax" comment) and I also tested it on my oc8 test deployment (and made sure  had really been run and minified some files).