[Gmod-ajax] created gbrowse-ajax-tiledimage tag

[Mitch S. <mit...@be...>]

Since I'm going to go ahead with some fairly invasive changes, I've 
created a tag in the server directory that marks the current TiledImage 
approach.

Also, just before that, I committed a change that fixes the right end of 
plus strand genes.  At some point I intend to update the demo with new 
images but it's not at the top of my list.

Mitch