-Codechange: Drop DirectoryReader use in ConfigFile::LoadFromDirectoryList. (PovAddictW)

It was using a DirectoryReader but not reading any directory, just using
its methods to concatenate a filename to a directory path and to check if
the final path was a file, which didn't make much sense.

Instead, add new functions in fileio separate from DirectoryReader
to test if a path is a file or a directory.



git-svn-id: https://freerct.googlecode.com/svn/trunk@1122 d3bf82d2-0c16-e458-5408-27be57bd1276
List files explicitly in CMakeLists instead of using GLOBs.
Split fileio.cpp into fileio_common and fileio_unix.

UnixDirectoryReader was moved to fileio_unix.cpp. This prepares for adding a
WindowsDirectoryReader in a fileio_win.cpp in the future.