Fix hg push and hg push -r sometimes creating new heads without --force. Fixing issue179. The algorithm checks if there not more new heads on the remote side than heads which become non-heads due to getting children. Pushing this repo: m /\ 3 3a| |/ / 2 2a |/ 1 to a repo only having 1, 2 and 3 didn't abort requiring --force before. Added test cases for this and some doc strings for used methods.

#!/bin/sh

mkdir a
cd a
hg init
echo 123 > a
hg add a
hg commit -m "a" -u a -d "1000000 0"

cd ..
mkdir b
cd b
hg init
echo 321 > b
hg add b
hg commit -m "b" -u b -d "1000000 0"

hg pull ../a
hg pull -f ../a
hg heads