Fix SF #659228, 'realpath' function missing from os.path

Also added realpath = abspath for os2emx, similar to windows/mac
which also don't really implement realpath.

Backport candidate, I think?
diff --git a/Lib/macpath.py b/Lib/macpath.py
index ba9d40b..e3145da 100644
--- a/Lib/macpath.py
+++ b/Lib/macpath.py
@@ -7,7 +7,7 @@
            "basename","dirname","commonprefix","getsize","getmtime",
            "getatime","getctime", "islink","exists","isdir","isfile",
            "walk","expanduser","expandvars","normpath","abspath",
-           "supports_unicode_filenames"]
+           "realpath","supports_unicode_filenames"]
 
 # Normalize the case of a pathname.  Dummy in Posix, but <s>.lower() here.