Special case printing -0

Use the 1/x trick to determine if a value is -0 and special case the
printing of it.

[closes #496]

src/core/PrettyPrinter.js

@@ -11,6 +11,8 @@ getJasmineRequireObj().pp = function(j$) {
         this.emitScalar('undefined');
       } else if (value === null) {
         this.emitScalar('null');
+      } else if (value === 0 && 1/value === -Infinity) {
+        this.emitScalar('-0');
       } else if (value === j$.getGlobal()) {
         this.emitScalar('<global>');
       } else if (value.jasmineToString) {