patch 7.4.1903

Problem:    When writing viminfo merging current history with history in
            viminfo may drop recent history entries.
Solution:   Add new format for viminfo lines, use it for history entries.  Use
            a timestamp for ordering the entries. Add test_settime().
            Add the viminfo version.  Does not do merging on timestamp yet.

src/structs.h

@@ -1014,6 +1014,7 @@ typedef struct
 #ifdef FEAT_MBYTE
     vimconv_T	vir_conv;	/* encoding conversion */
 #endif
+    int		vir_version;	/* viminfo version detected or -1 */
     garray_T	vir_barlines;	/* lines starting with | */
 } vir_T;