fix(angular.copy): change angular.copy to correcly clone RegExp

angular.copy previously copied RegExp as an empty object. Change detects
RegExp instance and clones into new RegExp. This change is based on a previous
fix to allow Date to be copied.

Closes #3473
Closes #3474
docs(httpBackend): update documentation for expect methods

`expect` methods can receive an Object as the data parameter, which was
undocumented.