Fixed #11919 -- Added a DPASTE_URL setting to customize the dpaste featu...

...re.

https://code.djangoproject.com/ticket/11919
It's not the simplest solution, but what do you think about the following proposal?:

* Make the current form a Django form
* Add `DEBUG_PASTEBIN_POST_URL` (default value is `'http://dpaste.com/'`) and `DEBUG_PASTEBIN_FORM` (default value is `'django.views.debug.PastebinForm'` or a better location)
* Subclass it in your project and set `DEBUG_PASTEBIN_POST_URL` to `'http://custompastebin.org/post'` and `DEBUG_PASTEBIN_FORM` to `'myproject.forms.MyCustomForm'`

Or we can change the above proposal to use their APIs.