patch 8.0.0647: syntax highlighting can make cause a freeze

Problem:    Syntax highlighting can make cause a freeze.
Solution:   Apply 'redrawtime' to syntax highlighting, per window.
diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index b310b9f..4a775fc 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -1,4 +1,4 @@
-*options.txt*	For Vim version 8.0.  Last change: 2017 Jun 13
+*options.txt*	For Vim version 8.0.  Last change: 2017 Jun 18
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -5945,10 +5945,14 @@
 			{only available when compiled with the |+reltime|
 			feature}
 	The time in milliseconds for redrawing the display.  This applies to
-	searching for patterns for 'hlsearch' and |:match| highlighting.
+	searching for patterns for 'hlsearch', |:match| highlighting an syntax
+	highlighting.
 	When redrawing takes more than this many milliseconds no further
-	matches will be highlighted.  This is used to avoid that Vim hangs
-	when using a very complicated pattern.
+	matches will be highlighted.
+	For syntax highlighting the time applies per window.  When over the
+	limit syntax highlighting is disabled until |CTRL-L| is used.
+	This is used to avoid that Vim hangs when using a very complicated
+	pattern.
 
 						*'regexpengine'* *'re'*
 'regexpengine' 're'	number	(default 0)