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.

#!/bin/sh
hg init
echo This is file a1 > a
hg add a
hg commit -m "commit #0" -d "1000000 0"
ls
echo This is file b1 > b
hg add b
hg commit -m "commit #1" -d "1000000 0"
hg co 0
# B should disappear
ls