Linux: Rename "Makefiles", clean them up a bit.

-> Shorter names without useless and outdated _ubuntugutsy postfix.
-> Help text describes actual purpose of the files.
-> Better error checking and tidying up.
Screen: Make timestamp check for OpenML/OS-Builtin method slightly more paranoid.

So far we didn't check for swap completion timestamps before swap was scheduled
if the swap was scheduled via normal bufferswap call, instead of osspecific_asyncflip.

Add a check for this as well.

-> Screen for 64-Bit Octave on Linux rebuilt.