patch 7.4.1574

Problem:    ":undo 0" does not work. (Florent Fayolle)
Solution:   Make it undo all the way. (closes #688)

src/testdir/test_alot.vim

@@ -4,6 +4,7 @@
 source test_assign.vim
 source test_cursor_func.vim
 source test_delete.vim
+source test_ex_undo.vim
 source test_expand.vim
 source test_feedkeys.vim
 source test_file_perm.vim

src/testdir/test_undolevels.vim

@@ -1,7 +1,5 @@
 " Tests for 'undolevels'
 
-set nocompatible viminfo+=nviminfo
-
 func FillBuffer()
   for i in range(1,13)
     put=i

src/undo.c

@@ -2286,6 +2286,13 @@ undo_time(
      * Init "closest" to a value we can't reach. */
     if (absolute)
     {
+	if (step == 0)
+	{
+	    /* target 0 does not exist, got to 1 and above it. */
+	    target = 1;
+	    above = TRUE;
+	}
+	else
 	    target = step;
 	closest = -1;
     }

src/version.c

@@ -743,6 +743,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1574,
 /**/
     1573,
 /**/