pull: add source information to the transaction
The source information can, should be applied once when opening the transaction
for the pull. This will lets element processed within a bundle2 be aware of them
and open the door to running a set of hooks when closing this pull transaction.
This is similar to what is done in server's unbundle call.
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown