fix($resource): correctly unescape /\. even if \. comes from a param value

Closes #15627

src/ngResource/resource.js

@@ -590,11 +590,12 @@ angular.module('ngResource', ['ng']).
             url = url.replace(/\/+$/, '') || '/';
           }
 
-          // then replace collapse `/.` if found in the last URL path segment before the query
-          // E.g. `http://url.com/id./format?q=x` becomes `http://url.com/id.format?q=x`
+          // Collapse `/.` if found in the last URL path segment before the query.
+          // E.g. `http://url.com/id/.format?q=x` becomes `http://url.com/id.format?q=x`.
           url = url.replace(/\/\.(?=\w+($|\?))/, '.');
-          // replace escaped `/\.` with `/.`
-          config.url = protocolAndIpv6 + url.replace(/\/\\\./, '/.');
+          // Replace escaped `/\.` with `/.`.
+          // (If `\.` comes from a param value, it will be encoded as `%5C.`.)
+          config.url = protocolAndIpv6 + url.replace(/\/(\\|%5C)\./, '/.');
 
 
           // set params - delegate param encoding to $http

test/ngResource/resourceSpec.js

@@ -1456,6 +1456,18 @@ describe('basic usage', function() {
         $httpBackend.expect('POST', '/users/.json').respond();
         $resource('/users/\\.json').save({});
       });
+      it('should work with save() if dynamic params', function() {
+        $httpBackend.expect('POST', '/users/.json').respond();
+        $resource('/users/:json', {json: '\\.json'}).save({});
+      });
+      it('should work with query() if dynamic params', function() {
+        $httpBackend.expect('GET', '/users/.json').respond();
+        $resource('/users/:json', {json: '\\.json'}).query();
+      });
+      it('should work with get() if dynamic params', function() {
+        $httpBackend.expect('GET', '/users/.json').respond();
+        $resource('/users/:json', {json: '\\.json'}).get();
+      });
     });
   });