Bug: the uploads page showed a remote size of 146 bytes for Pixiv uploads.
Cause: we didn't spoof the Referer header when making the HEAD request
for the image, causing Pixiv to return a 403 error.
Also fix the case where the Content-Length header is absent.
* Fix preview images not being resized to fit the screen when using the
bookmarklet.
* Fit images to both screen width and height by default. Previously we
fit to screen width only, so tall images were hard to see.
* Allow clicking on the image or pressing Z to toggle image size.
* Move size information to above the image and add resize links:
** small: fit width and height
** large: fit width
** full: fit none
* Bind the image error handler in an onerror attribute on the image
itself so that it will always fire. Before it wouldn't fire if the image
failed immediately on pageload before we could bind the error handler.
Don't send the referer when hotlinking preview images on the
/uploads/new page. Improves user privacy and may bypass anti-hotlinking
protections in some cases.
* On the /uploads/new page, instead of just showing a "This post has
probably already been uploaded" message, show the actual thumbnails of
posts having the same source as what the user is trying to upload.
* Move the iqdb results section up top, beside the related posts section.
This means that the preview will work even when the user doesn't use the
direct image link. e.g. The user can use the bookmarklet on Pixiv
mode=medium pages.
