How to specify headers parameter for custom Angular $resource action

I have confirmed that 1.1.3 does indeed support this. However, you need to make sure you also get the 1.1.3 version of the resource service. A quick test of:

angular.module('myApp', ['ngResource']).
  config(['$routeProvider', function($routeProvider) {
    $routeProvider.when('/', {templateUrl: 'partials/partial1.html',controller: 'MyController'});
    $routeProvider.otherwise({redirectTo: '/'});
  }])

  .controller("MyController", function( $scope, Bug) {
    Bug.post({test:"test"});
  })

  .factory('Bug', function($resource){
    var resource = $resource('/bug',{},{
        post:{
            method:"POST",
            isArray:false,
            headers:{'Content-Type':'application/x-www-form-urlencoded; charset=UTF-8'} 
        },
    });
    return resource;
});

This will make a request with the headers set to (confirmed using Chrome):

Content-Type:application/x-www-form-urlencoded; charset=UTF-8

A quick note, I was unable to find a download of the angular-resource.js, so I had to go the the github website to download it. It is here.

For some giggles, I created a fiddle. Notice that there will be a failed POST call, but its headers are set correctly. Example Fiddle

While the development docs (as of 12 Oct) show that overriding headers is possible in a $resource, it hasn't yet been released (v1.0.2 or v1.1.0). The feature is in the v1.0.x and master branches, however. In order to get at that feature, you might consider building from the v1.0.x branch for now.

How to build: http://docs.angularjs.org/#H1_4

Alternatively, you could pull from the snapshot build: http://code.angularjs.org/snapshot/

Looks like this feature will be in the next release.

Just adding the link to the 1.1.5 resource files (and others): http://code.angularjs.org/1.1.5/

You can set the URL to match the version you are looking for.
e.g. 1.1.4: http://code.angularjs.org/1.1.4/