tests/test-pull-permission

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 foo > b
hg add b
hg ci -m "b" -d "1000000 0"

chmod -w .hg

cd ..

hg clone a b

chmod +w a/.hg # let test clean up

cd b
hg verify