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.
#!/bin/sh
# initial
hg init test-a
cd test-a
cat >test.txt <<"EOF"
1
2
3
EOF
hg add test.txt
hg commit -m "Initial" -d "0 0"
# clone
cd ..
hg clone test-a test-b
# change test-a
cd test-a
cat >test.txt <<"EOF"
one
two
three
EOF
hg commit -m "Numbers as words" -d "0 0"
# change test-b
cd ../test-b
cat >test.txt <<"EOF"
1
2.5
3
EOF
hg commit -m "2 -> 2.5" -d "0 0"
# now pull and merge from test-a
hg pull ../test-a
HGMERGE=merge hg update -m
# resolve conflict
cat >test.txt <<"EOF"
one
two-point-five
three
EOF
rm -f *.orig
hg commit -m "Merge 1" -d "0 0"
# change test-a again
cd ../test-a
cat >test.txt <<"EOF"
one
two-point-one
three
EOF
hg commit -m "two -> two-point-one" -d "0 0"
# pull and merge from test-a again
cd ../test-b
hg pull ../test-a
HGMERGE=merge hg update --debug -m
cat test.txt | sed "s% .*%%"
hg debugindex .hg/data/test.txt.i
hg log