imgur.com fix for imgur.com/gallery/ links.

It used to assume the link was to a single-image gallery, and
directly display the corresponding jpg.  But occasionally the link is
to a gallery of an album, and the generated link is to an unrelated image.

To avoid that problem, we display /gallery/ links using
OthersIndirect, which gets the right result in both cases,
but is slower.
Experimental support for webm video format.

Works e.g. on 4chan.

Limitations:

This quick hack prevents non-webm images from displaying
(eg png, jpg).

Webm video sometimes shows the first frame for a long time before
starting playback; may be waiting for entire movie to load or at
least a substantial portion.

Controls aren't visible or useable.  Can't tell progress
while waiting to load; can't tell how much longer the movie
is while playing.

resizing with -, +, 0 doesn't work.
Fixed to support both images and webm.

Fixes long pause before starts playing.  Fixes video size.

Note that plays from webm links but not embedded <video> tags.

On some videos (high res?) seems to play at lower rate or skip frames:
video is less smooth than when webm is loaded into its own tab.
Added gfycat.com using webm format.

The site hosts each movie as gif, webm, etc.; TZP displays
it using the webm version.  Requires OthersIndirect to be on.

This site is often linked from reddit.com