Check @linkhere usage. Stricter parens checking.

ChangeLog

 2001-04-28  Per Cederqvist  <ceder@moria>
 
+	Check @linkhere usage.  Stricter parens checking.
+	* doc/checkargs.py (reader.check_paren_null): New name for former
+	check_paren_eof.  All callers updated.  Clear __parenstack, so
+	that errors are reported only once.
+	(lexer.__init__): Initialize __linkhere.
+	(lexer.toplevel_node): Check that no @linkhere or closing
+	parenthesis are pending.
+	(lexer.toplevel_reqdlink, lexer.__assert_no_linkhere) 
+	(lexer.toplevel_linkhere): New methods.
+
 	Renamed modify_server_info to modify_system_info, to match
 	Protocol-A.texi.
 	* src/include/services.h (modify_system_info): New name for former