This fixes the caching problem http://golem.ph.utexas.edu/instiki/show/Known+Bugs?rev=13#Caching which afflicts some installations of 0.16.3. With the patch, it's no longer necessary that the Instiki directory be owned by the instiki user (yay!).
Textile and RDoc users can't see the SVG anyway, so don't bother rendering it.
… check for other possible missing dirs.
On Webs with file uploads enabled, uploaded files were stored (in version 0.16.1 and earlier) in the public/ directory. This was a security threat. A miscreant could upload a .html file. When a user clicked on the link to the file, it was opened (unsanitized) in the browser. As of version 0.16.2, uploaded files are stored in the webs/ directory. Now, when the user clicks on the link, the file is sent with the Content-Disposition: attachment header set, which causes the file to be downloaded, rather than opened in the browser. As always, files downloaded from the internets should be treated with caution. At least, this way, they are not aoutomatically opened in the browser. To move your existing uploaded files to the new location, do a rake upgrade_instiki