Factor out common logic for Dot output format names/suffixes

Instead of having two `switch` statements on the Dot format
enumeration, give each Dot enumeration value a way to identify its own
preferred file suffix and command-line format name.  This removes some
warnings about `switch` statements without default cases.  It also
creates strong static enforcement that any new Dot format *must* also
provide this information.

com.ibm.wala.ide/src/com/ibm/wala/ide/ui/IFDSExplorer.java

@@ -77,19 +77,7 @@ public class IFDSExplorer {
       System.err.println("Domain:\n" + r.getProblem().getDomain().toString());
     }
 
-    String irFileName = null;
-    switch (DotUtil.getOutputType()) {
-    case PDF:
-      irFileName = "ir.pdf";
-      break;
-    case PS:
-    case EPS:
-      irFileName = "ir.ps";
-      break;
-    case SVG:
-      irFileName = "ir.svg";
-      break;
-    }
+    String irFileName = "ir." + DotUtil.getOutputType().suffix;
     String outputFile = scratchDirectory + File.separatorChar + irFileName;
     String dotFile = scratchDirectory + File.separatorChar + "ir.dt";
 

com.ibm.wala.util/src/com/ibm/wala/viz/DotUtil.java

@@ -20,7 +20,6 @@ import java.util.Iterator;
 
 import com.ibm.wala.util.WalaException;
 import com.ibm.wala.util.collections.Iterator2Collection;
-import com.ibm.wala.util.debug.Assertions;
 import com.ibm.wala.util.graph.Graph;
 
 /**
@@ -33,7 +32,16 @@ public class DotUtil {
    * 
    */
   public static enum DotOutputType {
-    PS, SVG, PDF, EPS
+    PS("ps"),
+    SVG("svg"),
+    PDF("pdf"),
+    EPS("eps");
+
+    public final String suffix;
+
+    DotOutputType(final String suffix) {
+      this.suffix = suffix;
+    }
   }
 
   private static DotOutputType outputType = DotOutputType.PDF;
@@ -51,19 +59,7 @@ public class DotUtil {
   }
 
   private static String outputTypeCmdLineParam() {
-    switch (outputType) {
-    case PS:
-      return "-Tps";
-    case EPS:
-      return "-Teps";
-    case SVG:
-      return "-Tsvg";
-    case PDF:
-      return "-Tpdf";
-    default:
-      Assertions.UNREACHABLE();
-      return null;
-    }
+    return "-T" + outputType.suffix;
   }
 
   /**