grep: display correct user/revision for --all in reverse.
Also handle multiple occurrences of the same line by storing
linestates in an array instead of a dict, and using difflib
to compute the difference between linestates.
changeset: 0:9426b370c206tag: tipuser: My Name <myname@example.com>date: Mon Jan 12 13:46:40 1970 +0000summary: commit-1