Do not corrupt documents without newline at EOF

Do not corrupt documents without newline at EOF

trim_eol() assumes that a line always ends either with \n, \r, or \r\n.
This assumption is always valid except for the last line of a document, since it
may miss the trailing newline. LyX does not create such documents, bu they may
result from automatic creation tools, and LyX can read them, so lyx2lyx should
be able to read them as well.
(cherry picked from commit c75c6e446a8bc0dbaabaf156c0abfd622c050129)

Fix the fix

MAC-style (pre-OS X) line ends were not recognized anymore
(cherry picked from commit 55af9cb006563032e35fcc8bc5c8c1284c0344da)