patch 8.1.1275: cannot navigate to errors before/after the cursor

Problem:    Cannot navigate to errors before/after the cursor.
Solution:   Add the :cbefore and :cafter commands. (Yegappan Lakshmanan,
            closes #4340)
diff --git a/runtime/doc/quickfix.txt b/runtime/doc/quickfix.txt
index 1f28f9b..ef084fa 100644
--- a/runtime/doc/quickfix.txt
+++ b/runtime/doc/quickfix.txt
@@ -152,8 +152,36 @@
 			exceeds the number of entries below the current line,
 			then the last error in the file is selected.
 
-							*:lbe* *:lbelow*
-:[count]lbe[low]	Same as ":cbelow", except the location list for the
+							*:lbel* *:lbelow*
+:[count]lbel[ow]	Same as ":cbelow", except the location list for the
+			current window is used instead of the quickfix list.
+
+							*:cbe* *:cbefore*
+:[count]cbe[fore]	Go to the [count] error before the current cursor
+			position in the current buffer.  If [count] is
+			omitted, then 1 is used.  If there are no errors, then
+			an error message is displayed.  Assumes that the
+			entries in a quickfix list are sorted by their buffer,
+			line and column numbers.  If [count] exceeds the
+			number of entries before the current position, then
+			the first error in the file is selected.
+
+							*:lbef* *:lbefore*
+:[count]lbef[ore]	Same as ":cbefore", except the location list for the
+			current window is used instead of the quickfix list.
+
+							*:caf* *:cafter*
+:[count]caf[ter]	Go to the [count] error after the current cursor
+			position in the current buffer.  If [count] is
+			omitted, then 1 is used.  If there are no errors, then
+			an error message is displayed.  Assumes that the
+			entries in a quickfix list are sorted by their buffer,
+			line and column numbers.  If [count] exceeds the
+			number of entries after the current position, then
+			the last error in the file is selected.
+
+							*:laf* *:lafter*
+:[count]laf[ter]	Same as ":cafter", except the location list for the
 			current window is used instead of the quickfix list.
 
 							*:cnf* *:cnfile*