selmiak: There's nothing in there at all unfortunately.
I'm positioning a clickable image relative to the centered main page, offset to the left.
The div containing the image is positioned in relation to an empty div at the top of the main page, but this latter one isn't at the top, it gets moved down by the whitespace.
I've uploaded the files here: http://db.tt/ALWyuuB
Here's a live version: http://home.pages.at/choala/whitespace/
If you look at that using Chrome, right-click the little picture and select "Inspect element", you'll immediately notice the spaces.
The thing is, I tried to move around the divs encompassing the image; they used to be outside the included file. It seems like the whitespace is always inserted right before/at "<?php".
But, like I said, this doesn't happen anywhere else on the page.Edit:
As a final test, I removed the php part and manually inserted the code supposed to be included; this of course fixes the problem, regardless of empty lines and tabs in between. Damn.