DebugStream update

[David Philippi]

Hi all

I've just implemented operator() (int) into DebugStream. It's intended to be 
used with the old PINGUS_DEBUG_X constants and checked against 
pingus_debug_flags. If the flag is not set, a special stream just consuming 
it's arguments is returned so that debug calls shouldn't be a big 
performance hit if the flag is not set.
Since I'm not very familar with streams, I invite anyone to test wheter 
everything works as intended or not. I've done some small test which worked 
flawless.

Bye David