require that snps be biallelic before we pass them to the TiTv calculation.

git-svn-id: file:///humgen/gsa-scr1/gsa-engineering/svn_contents/trunk@3316 348d0f76-0448-11de-a6fe-93d51630548a

java/src/org/broadinstitute/sting/gatk/walkers/varianteval/SimpleMetricsByAC.java

@@ -143,6 +143,7 @@ public class SimpleMetricsByAC extends VariantEvaluator {
 
         if (eval != null &&
                 eval.isSNP() &&
+                eval.isBiallelic() &&
                 eval.hasGenotypes()) {
             if ( metrics == null )
                 metrics = new MetricsByAc(2 * eval.getNSamples());