change accountSwitcher.js to always use SSL

Move all accountSwitcher login requests to HTTPS and stop using ssl.reddit.com.

(fixes account switcher for Chrome incognito)

Formerly accountSwitcher.js used an unsecured request to www.reddit.com to log in when in Chrome incognito mode, as ssl.reddit.com cookies were not allowed. Now that reddit supports HTTPS site-wide, that call is blocked (as it should be) and unnecessary, as plain reddit.com can be accessed via HTTPS.

See https://www.reddit.com/r/RESissues/comments/2gcsi1/bug_account_switcher_loads_nonhttps_api_login/
Remove the now-unused BrowserStrategy.supportsThirdPartyCookies()
Allow Firefox to log in securely from unsecure HTTP://reddit.com

This is necessary because Firefox treats requests from HTTP --> HTTPS
on the same domain as a cross-site request and blocks cookies from it
unless the withCredentials flag is set on the call.

See https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS#Requests_with_credentials

This does *not* fix the issue for Opera, although adding a similar line
to the Opera code will probably work.
make accountSwitcher.js send an isLogin flag

This is necessary so that we can set a CORS
withCredentials flag on the AJAX call, otherwise
some browsers (Firefix, apparently Opera) will
block the cookies if we try to log in from
unsecure http://reddit.com.
spaces --> tabs
Add CORS withCredentials flag to Opera

(Port of the Firefox fix from below.)

Tested Opera 12 / Opera 12 private tab/window.
Merge pull request #1620 from calvinli/master

change accountSwitcher.js to always use HTTPS