patch 8.0.1023: it is not easy to identify a quickfix list

Problem:    It is not easy to identify a quickfix list.
Solution:   Add the "id" field. (Yegappan Lakshmanan)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index a75d4f6..ecb41c4 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -4632,6 +4632,9 @@
 		returns only the items listed in {what} as a dictionary. The
 		following string items are supported in {what}:
 			context	get the context stored with |setqflist()|
+			id	get information for the quickfix list with
+				|quickfix-ID|; zero means the id for the
+				current list or the list specifed by 'nr'
 			items	quickfix list entries
 			nr	get information for this quickfix list; zero
 				means the current quickfix list and '$' means
@@ -4646,6 +4649,8 @@
 			all	all of the above quickfix properties
 		Non-string items in {what} are ignored.
 		If "nr" is not present then the current quickfix list is used.
+		If both "nr" and a non-zero "id" are specified, then the list
+		specified by "id" is used.
 		To get the number of lists in the quickfix stack, set 'nr' to
 		'$' in {what}. The 'nr' value in the returned dictionary
 		contains the quickfix stack size.
@@ -4657,6 +4662,7 @@
 
 		The returned dictionary contains the following entries:
 			context	context information stored with |setqflist()|
+			id	quickfix list ID |quickfix-ID|
 			items	quickfix list entries
 			nr	quickfix list number
 			title	quickfix list title text
@@ -7069,6 +7075,7 @@
 				text and add the resulting entries to the
 				quickfix list {nr}.  The value can be a string
 				with one line or a list with multiple lines.
+		    id		quickfix list identifier |quickfix-ID|
 		    items	list of quickfix entries. Same as the {list}
 				argument.
 		    nr		list number in the quickfix stack; zero
@@ -7079,6 +7086,9 @@
 		If the "nr" item is not present, then the current quickfix list
 		is modified. When creating a new quickfix list, "nr" can be
 		set to a value one greater than the quickfix stack size.
+		When modifying a quickfix list, to guarantee that the correct
+		list is modified, 'id' should be used instead of 'nr' to
+		specify the list.
 
 		Examples: >
 			:call setqflist([], 'r', {'title': 'My search'})