Add the settabvar() and gettabvar() functions.

Various runtime file updates.

runtime/doc/usr_04.txt

@@ -498,7 +498,7 @@ else:
 	~	change case of the character under the cursor, and move the
 		cursor to the next character.  This is not an operator (unless
 		'tildeop' is set), thus you can't use it with a motion
-		command.  It does works in Visual mode and changes case for
+		command.  It does work in Visual mode and changes case for
 		all the selected text then.
 
 	I	Start Insert mode after moving the cursor to the first