Compile fixes for Linux

Hi,

 Trying to compile openwm under linux, I had to fix a few compilation errors.
Relevant system informations: Gentoo Linux
gcc (Gentoo 4.7.3-r1 p1.4, pie-0.5.5)
boost 1.52

I hope these fixes are compatible with other architectures.

I heard about openmw yesterday, I could not wait to try it on my box (despite the compile errors...). What you have done is impressive! (it reminds me of all the lost nights playing that game :) )