query_classifier.cc: query_is_parsed is now global function and can be used to check whether parsing information already exists in the buffer.
skygw_utils.cc: removed replace_str and implemented replace_literal which replaces user-provided literals in query with predefined string "?". Replacing is done one by one, so it is suboptimal ipmlementation since all literals could be passed to replacement function in one call and processed all before returning.
Fixed comment.
query_classifier.cc: cleaned up and simplified skygw_get_canonical
skygw_util.cc:fixed memory allocation issue where terminating byte wasn't counted. Added some error checks.
skygw_get_canonical didn't return NULL pointerin cases where parsing info didn't exist or something went wrong.
Merge remote-tracking branch 'maxscale/MAX-160' into dev