The modern pager API is to use ui.pager() explicitly just before the time
a command needs a pager. It's now hard-coded in individual commands, and
opt-in by default. Users wanting to disable pagers for certain commands need
to disable them explicitly. Ideally we don't need the pager extensions or
the pager.attend setting.
This patch migrates show, smartlog, fastannotate, and grep to use
the modern API.