Updated engine.pot.
Updated swedish translate from updated pot file.
Merge pull request #335 from hean01/master

Updated engine.pot file and corresponding swedish translation.
Merge pull request #337 from stefanbeller/master

Change IRC channel in travis file.
Setup size of backgroundsurface depending on rerender distance.

When animated_tiles is switched off, the background will be rendered
into a static image and only renewed, when the player has moved a certain
distance specified in 'movedistance_to_rerender'.
Use this variable as well for the dimensions of the background surface.

Fixes #333