fix($injector): report circularity in circular dependency error message

Change the error message for a circular dependency to display the full
circle back to the first service being instantiated, so that the problem
is obvious. The previous message stopped one dependency short of the full
circle.

Changes the content of the cdep error message, which may be considered
a breaking change.

Closes #7500

src/auto/injector.js

@@ -724,7 +724,8 @@ function createInjector(modulesToLoad) {
     function getService(serviceName) {
       if (cache.hasOwnProperty(serviceName)) {
         if (cache[serviceName] === INSTANTIATING) {
-          throw $injectorMinErr('cdep', 'Circular dependency found: {0}', path.join(' <- '));
+          throw $injectorMinErr('cdep', 'Circular dependency found: {0}',
+                    serviceName + ' <- ' + path.join(' <- '));
         }
         return cache[serviceName];
       } else {

test/auto/injectorSpec.js

@@ -630,7 +630,7 @@ describe('injector', function() {
             $provide.factory('service', function(service){});
             return function(service) {};
           }]);
-        }).toThrowMinErr('$injector', 'cdep', 'Circular dependency found: service');
+        }).toThrowMinErr('$injector', 'cdep', 'Circular dependency found: service <- service');
       });
 
 
@@ -641,7 +641,7 @@ describe('injector', function() {
             $provide.factory('b', function(a){});
             return function(a) {};
           }]);
-        }).toThrowMinErr('$injector', 'cdep', 'Circular dependency found: b <- a');
+        }).toThrowMinErr('$injector', 'cdep', 'Circular dependency found: a <- b <- a');
       });
 
     });