The class PLRuby::Tinterval implement the PostgreSQL type tinterval
Convert a String (PostgreSQL representation) to a Tinterval
create a Tinterval with the 2 Time objects low and high
return a Time which is the high value of the interval
set the high value for the interval
return a Time which is the low value of the interval
set the low value for the interval
return the string representation of the object
[Validate]