check_dns: add AAAA,MX,TXT,SRV,CNAME

Just turning attached patch of github issue #894 into a push request.
plugins/check_dns.c: Authoritative response change

Altered output for authoritative message if no dns server was provided, in case of using -A without -s.
plugins/check_dns.c: Authoritative bool and logic

Flipped non_authoritative to be a logical use of true\false instead of inverse logic. Corrected use of -A so that it was respected properly and errors if non-auth responses are found.
utils.h, utils.c - Additions to change string case

Adds strntolower() and strntoupper() to allow changing of string case when user input is incorrect or for comparison. These work on the given string in memory and do not return a new string that has been changed.
check_dns.c querytype additions, check corrections

Additions of several query types, case insensitive query types, validation of type received vs requested.

TODO: limit and validate TXT records to correct size per rfc standards.
Merge branch 'maint' of github.com-sreinhardt:nagios-plugins/nagios-plugins into maint