(reader.__init__): Initialise __parenstack, __errfound and __quoted.
(reader.error, reader.errfound): New methods.
(reader.ungetc, reader.getc_eofok): Handle quoting and parens nesting.
(reader.check_paren_eof): Report unbalanced parens at EOF.
(lexer.__init__): Moved __errfound to the reader class.
(lexer.run): Check for unbalanced parens at EOF.
(lexer.toplevel_reqlink): Ignore.
(lexer.toplevel_reqdlink, lexer.toplevel_linkhere): Ignore, for
	now.  We should check nesting et c of these.
(lexer.toplevel_unmacro): Ignore.
(lexer.error): Moved the implementation to the reader class.  This
	is only a wrapper.