edd_ajax_apply_discount fix

When calling 'edd_ajax_apply_discount' via ajax, response fails with the
following messages:

Notice:  Undefined variable: key in
..\easy-digital-downloads\includes\discount-functions.php on line 761
Notice:  Undefined variable: value in
...\easy-digital-downloads\includes\discount-functions.php on line 762

In ajax-function.php on line 164 there is a call to
edd_is_discount_valid() without passing a user. That function later
calls edd_is_discount_used() which failed because no user is sent.
Remove version check from sequential upgrades routine. #2345
Merge branch 'master' of github.com:easydigitaldownloads/Easy-Digital-Downloads
Merge pull request #2346 from somewebmedia/master

edd_ajax_apply_discount fix
Fix issue with double s in checkout URI. #2348
Added total and subtotal values to some ajax returns

Added total value to ajax return when adding or removing item from cart,
and subtotal value when updating item quantity.
In case discounts are already applied we need both total and subtotal
values returned for these actions.
Missing comma to previous push
Merge pull request #2349 from somewebmedia/master

Added total and subtotal values to some ajax returns
Update test_remove_item_from_cart() for #2349
Merge branch 'master' of github.com:easydigitaldownloads/Easy-Digital-Downloads
Add additional discount actions. #2240
Minify global checkout JS
Check if failure_page is empty before proceeding in edd_listen_for_failed_payments(). #2353
Replace preview email data with current user data
Apply 100% width to Chosens added dynamically

When clicking the "Insert Download" button in the WordPress for an editor that is dynamically added to the edit screen, the select box is broken because the CSS fix is not applied to the select box. This issue is caused by the event being improperly delegated. By binding the event to `#post`, it will be applied to WordPress editors that are added dynamically.

Additionally, the `$('#choose-download .edd-select-chosen')` is an inefficient selector and has been improved (test http://jsperf.com/jquery-selector-race).
Merge pull request #2356 from tollmanz/master

Apply 100% width to Chosens added dynamically.
fix: undefined index
Merge pull request #2357 from sumobi/master

fix: undefined index on tools -> system info
Respect ENforce SSL option in payment icons> #2358
Eliminate use of extract() from edd_render_file_row(). #2359