Make string juxtaposition combine properly with string interpolations.

frog/leg/ssa/builder.dart

Index: frog/leg/ssa/builder.dart
diff --git a/frog/leg/ssa/builder.dart b/frog/leg/ssa/builder.dart
index 3152bf2f748e8f279acf4ce96b379d87f6caa534..10e8c68282015b59edeeb7d981beb5859ea9b006 100644
--- a/frog/leg/ssa/builder.dart
+++ b/frog/leg/ssa/builder.dart
@@ -1325,7 +1325,7 @@ class SsaBuilder implements Visitor {
       if (folded !== null) {
         stack.add(graph.addConstant(folded));
         return;
-      }      
+      }
     }
     HInstruction target =
         new HStatic(interceptors.getPrefixOperatorInterceptor(op));
@@ -1640,7 +1640,7 @@ class SsaBuilder implements Visitor {
           list.add(namedArguments[foundIndex]);
         } else {
           Constant constant = compiler.compileVariable(parameter);
-          list.add(graph.addConstant(constant)); 
+          list.add(graph.addConstant(constant));
         }
       }
     }
@@ -2281,6 +2281,7 @@ class SsaBuilder implements Visitor {
     work.allowSpeculativeOptimization = false;
     visit(node.expression);
     HInstruction expression = pop();
+
     Link cases = node.cases.nodes;
     int count = 0;
     handleThen() {