Fix crash on attempt to save cached OpenGL nodes on OS X

Root permissions are required to be able to create directories inside /Library/Application Support
So user's ~/Library/Application Support is used to store cached nodes
- fixed: plane equation vectors must be normalized when being loaded from UDMF.
Fix crash when GL nodes file cannot be opened for writing

Report errors to console if nodes file cannot be opened or written
Remove redundant saving of GL nodes if they were loaded from cache
Merge branch 'master' of https://github.com/rheit/zdoom into osx
* change log and minor fixes in Read Me document
* anniversary version in .plist