Decodes modified UTF-7 text into ISO-8859-1 string.
Returns a string that is encoded in ISO-8859-1 and consists of the same sequence of characters in text, or FALSE if text contains invalid modified UTF-7 sequence or text contains a character that is not part of ISO-8859-1 character set. This function is needed to decode mailbox names that contain certain characters which are not in range of printable ASCII characters. The modified UTF-7 encoding is defined in RFC 2060, section 5.1.3 (original UTF-7 was defned in RFC1642).