Added IPv6 support for GeoIP location, while still retaining IPv4 functi...

IPv4 tracking depends on: 
- GEOIP_ADDR 
- GEOIP_CONTINENT_CODE 
- GEOIP_COUNTRY_CODE 
- GEOIP_COUNTRY_NAME 

And IPv6 depends on: 
GEOIP_ADDR 
GEOIP_CONTINENT_CODE_V6 
GEOIP_COUNTRY_CODE_V6 
GEOIP_COUNTRY_NAME_V6 

For the isAvailable() and isWorking() functions, added checks to see if the GEOIP_COUNTRY_CODE_V6 variable has been populated.

For getLocation, if each IPv4 variable is empty, check if the IPv6 equivalent is empty. If not, use the IPv6 equivalent instead.
There's a typo here (extra +)