merge: shortcircuit filemerge for identical files - use filectx.cmp to compare files - move merge messages into filemerge - kill the redundant resolving message - update tests

#!/bin/sh

hg init
touch a
hg add a
hg ci -m "a" -d "1000000 0"

echo 123 > b
hg add b
hg diff --nodates

hg diff --nodates -r tip

echo foo > a
hg diff --nodates