patch 8.1.0345: cannot get the window id associated with the location list

Problem:    Cannot get the window id associated with the location list.
Solution:   Add the "filewinid" argument to getloclist(). (Yegappan
            Lakshmanan, closes #3202)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index e838395..b8ab0f3 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -4729,6 +4729,10 @@
 		If the optional {what} dictionary argument is supplied, then
 		returns the items listed in {what} as a dictionary. Refer to
 		|getqflist()| for the supported items in {what}.
+		If {what} contains 'filewinid', then returns the id of the
+		window used to display files from the location list. This
+		field is applicable only when called from a location list
+		window.
 
 getmatches()						*getmatches()*
 		Returns a |List| with all matches previously defined by