added a check to ensure the eval track variation is bi-allelic. Also changed some string constants over to enums

git-svn-id: file:///humgen/gsa-scr1/gsa-engineering/svn_contents/trunk@1884 348d0f76-0448-11de-a6fe-93d51630548a

java/src/org/broadinstitute/sting/playground/gatk/walkers/varianteval/VariantEvalWalker.java

@@ -195,7 +195,7 @@ public class VariantEvalWalker extends RefWalker<Integer, Integer> {
         int nBoundGoodRods = tracker.getNBoundRodTracks("interval");
         if ( nBoundGoodRods > 0 ) {
             //System.out.printf("%s: n = %d%n", context.getLocation(), nBoundGoodRods );
-        
+
             // Iterate over each analysis, and update it
             Variation eval = (Variation)tracker.lookup("eval", null);