patch 8.1.1542: an OptionSet autocommand does not get enough info

Problem:    An OptionSet autocommand does not get enough info.
Solution:   Add v:option_command, v:option_oldlocal and v:option_oldglobal.
            (Latrice Wilgus, closes #4118)
diff --git a/runtime/doc/version8.txt b/runtime/doc/version8.txt
index 1dcef7e..73db5f0 100644
--- a/runtime/doc/version8.txt
+++ b/runtime/doc/version8.txt
@@ -336,7 +336,10 @@
 |v:null|		an empty String, used for JSON
 |v:option_new|    	new value of the option, used by |OptionSet|
 |v:option_old|    	old value of the option, used by |OptionSet|
+|v:option_oldlocal|	old local value of the option, used by |OptionSet|
+|v:option_oldglobal|	old global value of the option, used by |OptionSet|
 |v:option_type|   	scope of the set command, used by |OptionSet|
+|v:option_command|	command used to set the option, used by |OptionSet|
 |v:progpath|		the command with which Vim was invoked
 |v:t_bool|		value of Boolean type
 |v:t_channel|		value of Channel type