Fixes for various typos in code

**IMPORTANT**: On upgrading to RSpec 2.14, you will probably encounter one failure on executing specs with a full OpenProject.org plugin configuration. The relevant fixes are c66b959854050ae30659e3ad010fb7461d7b6eed, 88e8efe12eebb57ef9fdbb088e6cc7ef36f3f85f. I would recommend merging #1064 first, as that PR includes those patches.