Fix functional-test-105 failure in OSX.

See https://github.com/neovim/neovim/issues/1519 for failure report.

Cause    : In OSX, /tmp is a symbolic link to /private/tmp, which causes
           expected and got results different because of implicit
           resolution.
Solution : Resolve path before setting expected value.
Fix Makefile for running valgrind with old tests.
Merge pull request #1521 from three-comrades/valgrind

Fix Makefile for running valgrind with old tests.
Merge pull request #1520 from elmart/fix-func-tests

Fix functional tests failing on OSX.
Remove NeXTSTEP references

Remove trailing whitespace as well.
Remove Atari MiNT references
Remove OS/2 references

Paul Slootman was removed from the top of os_unix.c as OS/2 is no longer
supported, but is still credited in runtime/doc/intro.txt.