[RFC] vim-patch:7.4.528

```
Problem:    Crash when using matchadd() (Yasuhiro Matsumoto)
Solution:   Copy the match regprog.

https://code.google.com/p/vim/source/detail?r=v7-4-528
```

Original patch:
```diff
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -7588,6 +7588,12 @@ next_search_hl(win, shl, lnum, mincol, c
 	shl->lnum = lnum;
 	if (shl->rm.regprog != NULL)
 	{
+	    /* Remember whether shl->rm is using a copy of the regprog in
+	     * cur->match. */
+	    int regprog_is_copy = (shl != &search_hl && cur != NULL
+				&& shl == &cur->hl
+				&& cur->match.regprog == cur->hl.rm.regprog);
+
 	    nmatched = vim_regexec_multi(&shl->rm, win, shl->buf, lnum,
 		    matchcol,
 #ifdef FEAT_RELTIME
@@ -7596,6 +7602,10 @@ next_search_hl(win, shl, lnum, mincol, c
 		    NULL
 #endif
 		    );
+	    /* Copy the regprog, in case it got freed and recompiled. */
+	    if (regprog_is_copy)
+		cur->match.regprog = cur->hl.rm.regprog;
+
 	    if (called_emsg || got_int)
 	    {
 		/* Error while handling regexp: stop using this regexp. */
diff --git a/src/nvim/version.c b/src/nvim/version.c
--- a/src/nvim/version.c
+++ b/src/nvim/version.c
@@ -742,6 +742,8 @@ static char *(features[]) =
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    528,
+/**/
     527,
 /**/
     526,
```