fix warnings/errors detected by clang

As of this commit, we are now able to compile ost
(no gfx/no gui). Unittests are all passing and ost
starts up normally.

git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/trunk@2539 5a81b35b-ba03-0410-adc8-b2c5c5119f08