patch 8.0.1563: timeout of getwinposx() can be too short

Problem:    Timeout of getwinposx() can be too short. (lilydjwg)
Solution:   Add getwinpos(). (closes #2689)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 578e5d3..51f059f 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2192,8 +2192,9 @@
 gettabwinvar({tabnr}, {winnr}, {name} [, {def}])
 				any	{name} in {winnr} in tab page {tabnr}
 getwininfo([{winid}])		List	list of windows
-getwinposx()			Number	X coord in pixels of GUI Vim window
-getwinposy()			Number	Y coord in pixels of GUI Vim window
+getwinpos([{tmeout}])		List	X and Y coord in pixels of the Vim window
+getwinposx()			Number	X coord in pixels of the Vim window
+getwinposy()			Number	Y coord in pixels of the Vim window
 getwinvar({nr}, {varname} [, {def}])
 				any	variable {varname} in window {nr}
 glob({expr} [, {nosuf} [, {list} [, {alllinks}]]])
@@ -4878,16 +4879,24 @@
 			:let list_is_on = gettabwinvar(1, 2, '&list')
 			:echo "myvar = " . gettabwinvar(3, 1, 'myvar')
 <
+getwinpos([{timeout}])					*getwinpos()*
+		The result is a list with two numbers, the result of
+		getwinposx() and getwinposy() combined: 
+			[x-pos, y-pos]
+		{timeout} can be used to specify how long to wait in msec for
+		a response from the terminal.  When omitted 100 msec is used.
+
 							*getwinposx()*
 getwinposx()	The result is a Number, which is the X coordinate in pixels of
 		the left hand side of the GUI Vim window. Also works for an
-		xterm.
+		xterm (uses a timeout of 100 msec).
 		The result will be -1 if the information is not available.
 		The value can be used with `:winpos`.
 
 							*getwinposy()*
 getwinposy()	The result is a Number, which is the Y coordinate in pixels of
-		the top of the GUI Vim window.  Also works for an xterm.
+		the top of the GUI Vim window.  Also works for an xterm (uses
+		a timeout of 100 msec).
 		The result will be -1 if the information is not available.
 		The value can be used with `:winpos`.