Passes an 'index' magic number to the upload/save functions which
pass that back to the *Done callbacks, so we know if the *raw*
snapshot is still up to date when the upload succeeds or fails.
Need to test:
localassetbrowser
preview related floaters
hgfloatertexteditor
maps
media textures! Currently very hacky
web browser
alpha masks on avatars
bumpmaps
Are all sky components appearing?
LLViewerDynamicTexture (texture baking, browser, animated textures, anim previews, etc)
Snapshot related features
Customize avatar
vfs floater
UI textures in general
Texture priority issues
