Intrigued on why WPTouch was uploading files into
wp-content/blogs.dir/ when I'm using a Single Site installation, I just seen the motive:
You are detecting Multisite by the existence of the folder
This folder stands for Must Use plugin. It has nothing to do with the site being Multisite (the old MultiUser) or not.
The correct is to use the function
is_multisite(). You can completely drop the use of
compat_is_wordpress_mu and use that instead. I wrote some reference material on MS functions and plugin usage in this Stack Overflow answer.
Cheers and thanks for the amazing plug :o)
PS: I see that you still don't have a retina image in your
assets/ folder. Also note that all the plugins' screenshots can be moved to that folder, so as the make the package lighter for download.