Fix incorrect svn properties, for example .png should not have svn:keywords set, that could in worst case result in corruption. While we are updating properties anyway, clean up incorrect (but mostly harmless) svn:mime-type, svn:executable and so on.
git-svn-id: svn+ssh://svn.code.sf.net/p/crossfire/code/arch/trunk@13991 282e977c-c81d-0410-88c4-b93c2d0d6712