+0.0 and -0.0 result in PlusZero term

[Franck Cassez]

Problem: if +0.0/-0.0 is a Double: +0.0.asFloat64 generates the term ConstantTerm(FPBVPlusZero(11,53)) -0.0asFloat64 does the same: ConstantTerm(FPBVPlusZero(11,53))

Should be FPBVMinusZero(11,53) in the latter case.

Same problem occurs with Floats.

[Franck Cassez]

Create a PlusZero/MinusZero term according to the sign of 0.0.

Use equals to compare objects rather than values.

fixes #9

→ <<cset d8b00e95c9c4>>

[Franck Cassez]

Tests:

val pZeroDouble : Double = +0.0e0
val mZeroDouble : Double = -0.0e0
val pZeroFloat : Float = +0.0.toFloat
val mZeroFloat : Float = -0.0.toFloat

 pZeroDouble.asFloat64  generates  ConstantTerm(FPBVPlusZero(11,53))
 mZeroDouble.asFloat64  generates  ConstantTerm(FPBVMinusZero(11,53))
 pZeroFloat.asFloat32  generates  ConstantTerm(FPBVPlusZero(8,24))
 mZeroFloat.asFloat32  generates ConstantTerm(FPBVMinusZero(8,24))