query_classifier.cc:skygw_get_canonical: if the item to be replaced is an empty string "", it is processed differently from the other cases due to difficulties to get wanted result by adding special rule for that to regex.
query_classifier.h: added parsing information structure to query classifier away from buffer.h.
buffer.c:introduced a buffer object which includes object pointer and a clean-up call-back function. Buffer objects form a list which is cleaned up by the last referrer of the buffer, as a part of gwbuf_free. Buffer object list is protected by a spinlock gwbuf_lock.
	Also added identifier type, bufobj_id_t which is enumerated type and currently includes one value only, GWBUF_PARSING_INFO. Added also a bitfield for information about the buffer. It currently has one type only, GWBUF_INFO_PARSED indicating that buffer content is parsed and there is buffer object of type GWBUF_PARSING_INFO.
skygw_utils.cc:replace_literal:changed regexec matching to case insensitive because user-defined literals are sometimes converted to upper-case ones.