tests/test-issue842

keyword: avoid additional conflicts during merge/resolve

Make merge and resolve trigger kwtemplater.restricted to compare
data without keyword expansion.
The keyword stays outside the conflict:

$Keyword$
<<<<<<< local
bar
=======
foo
>>>>>>> other

and will again be expanded on commit.
Demonstrate in test case.

hg init test
cd test
echo foo > a
hg ci -Ama

hg up -r0000
echo bar > a
echo % should issue warning
hg ci -Amb

hg up -r0000
echo stuffy > a
echo % should not issue warning
hg ci -q -Amc

hg up -r0000
echo crap > a
hg branch testing
echo % should not issue warning
hg ci -q -Amd