make termination checker respect --solvers argument,

(but not timeout)

src/main/scala/leon/termination/Processor.scala

@@ -35,7 +35,7 @@ trait Solvable extends Processor {
     val sizeUnit    : UnitDef     = UnitDef(FreshIdentifier("$size"),Seq(sizeModule)) 
     val newProgram  : Program     = program.copy( units = sizeUnit :: program.units)
 
-    SolverFactory.default(context, newProgram).withTimeout(500.millisecond)
+    SolverFactory.getFromSettings(context, newProgram).withTimeout(500.millisecond)
   }
 
   type Solution = (Option[Boolean], Map[Identifier, Expr])