feat(http): add config parameter to headers functions

[grisendo]

Request Type: feature

How to reproduce:

Component(s): $http

Impact:

Complexity: small

This issue is related to:

Detailed Description:

Adds 'data' parameter in $http's header property when headers defined as functions

Other Comments:

This pull request adds to $http header functions a data parameter, so headers can use object properties to be built:

Example (in a $resource) :

...
                  login: {
                    url: './api/login.json',
                    method: 'POST',
                    headers : {
                        'Authorization': function(data) {
                          return 'Basic ' + btoa(data.user + ':' + data.pass);
                        }
                    },
...

[mary-poppins]

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[IgorMinar]

it might be better to pass in the config object since that one contains all of the information about the request. (other people might want to set a header depending on the http method or other header value)

we'll also need tests for this change.

[grisendo]

So now the example should be:

...
                  login: {
                    url: './api/login.json',
                    method: 'POST',
                    headers : {
                        'Authorization': function(config) {
                          return 'Basic ' + btoa(config.data.user + ':' + config.data.pass);
                        }
                    },
...

[pkozlowski-opensource]

@grisendo - I think that this is a reasonable request and I can see that you've already incorporated Igor's suggestion. This PR could land but it requires a bit more work before it can be merged:

• - it doesn't merge cleanly any more, could you please rebase it on top of the current master?
• - we need to update docs to reflect this new argument

Thnx!

[grisendo]

Just refactored, adding documentation later

[grisendo]

Added also documentation changes.

[grisendo]

Changed to 'config object' as @pkozlowski-opensource suggested and fixed a typo.

[grisendo]

What about 'requestConfig', since is the name given to 'function $http(requestConfig) {' in 'src/ng/http.js' line 619?