add prechangegroup and pretxnchangegroup hooks.
prechangegroup lets you stop push, pull or unbundle before it begins.
pretxnchangegroup lets you inspect changegroup before transaction is
committed, and roll back if you not like it.
# should show copy
copy: foo -> bar
# shouldn't show copy
# should match
rev offset length base linkrev nodeid p1 p2
0 0 5 0 0 2ed2a3912a0b 000000000000 000000000000
renamed from foo:2ed2a3912a0b24502043eae84ee4b279c18b90dd
# should not be renamed
not renamed
# should show copy
copy: foo -> bar
# should show no parents for tip
rev offset length base linkrev nodeid p1 p2
0 0 69 0 1 6ca237634e1f 000000000000 000000000000
1 69 6 1 2 7a1ff8e75f5b 6ca237634e1f 000000000000
2 75 82 1 3 243dfe60f3d9 000000000000 000000000000
# should match
rev offset length base linkrev nodeid p1 p2
0 0 5 0 0 2ed2a3912a0b 000000000000 000000000000
1 5 7 1 2 dd12c926cf16 2ed2a3912a0b 000000000000
renamed from foo:dd12c926cf165e3eb4cf87b084955cb617221c17
# should show no copies