Fix operator resolution case

An unresolved operator can be preceded by an operator of unknown arity, which means that the unresolved operator should most likely be a unary operator.
DDMathEvaluator.angleMeasurementMode.  Fixes issue #29.

DDMathEvaluator has a new property to specify that the arguments to the trigonometric functions should be interpreted as being in degrees versus radians (the default).
Merge branch 'master' of git://github.com/davedelong/DDMathParser