pager: provide a default attend list
The default list includes commands which normally print large amounts of
text. This should be more user-friendly than paging all commands by default,
which can be confusing when the pager swallows input prompts (with, e.g.,
record, merge, HTTP/SSH authentication, etc.)
# should print nothing
# should fail
abort: path 'b/x' is inside repo 'b'
abort: path 'b/x' is inside repo 'b'
# should fail
abort: path 'b/x' is inside repo 'b'
# should arguably print nothing
# should fail
abort: path 'b/a' is inside repo 'b'