Added isOne method
Added isOne method

isOne is very efficient for LongRational, and just returns
false for BigRational because Rational.one is always represented
as a LongRational due to the invariants.

JackSullivan/spire,tixxit/spire,siddhartha-gadgil/spire,tixxit/spire,adampingel/spire,JackSullivan/spire,adampingel/spire,rklaehn/spire,codeaudit/spire,guersam/spire,kevinmeredith/spire,non/spire,rklaehn/spire,codeaudit/spire,guersam/spire,kevinmeredith/spire,non/spire,siddhartha-gadgil/spire