VOL-44, VOL-55: Created new contact subtype Volunteer and an example cus...

...tom field for same. Includes both install and upgrade code.
would a better description be, fieldCreateResultValidateAndNotify()?
"And" is an indication that separate functions are called for. 
"handle" is an idiom for an event listener, which this is not technically. The name says little about what it does and instead when it is called.