patch 7.4.1008

Problem:    The OS/2 code pollutes the source while nobody uses it these days.
Solution:   Drop the support for OS/2.

src/window.c

@@ -6531,7 +6531,7 @@ vim_FullName(fname, buf, len, force)
 	/* something failed; use the file name (truncate when too long) */
 	vim_strncpy(buf, fname, len - 1);
     }
-#if defined(MACOS_CLASSIC) || defined(OS2) || defined(MSDOS) || defined(MSWIN)
+#if defined(MACOS_CLASSIC) || defined(MSDOS) || defined(MSWIN)
     slash_adjust(buf);
 #endif
     return retval;