Cannot advance to next image (Shift-PgDn) when viewing JPG

[Lewis Rosenthal]

Shift-PgDn? works as expected with all document types I've tested, except JPG, where the same image is simply reloaded. Shift-PgUp? *does* work, however, even on these files. (1.3.4b2)

I'm marking this as core, but it's liable to be in the JPG plugin; I don't know the code to make that determination.

PS - Need to add 1.3.4 beta releases to the Version dropdown in Trac.