Issue a warning if "-r ." is used with two working directory parents.
Rationale for not aborting instead:
The first parent is usually more important as it is the local branch
during a merge and commands like 'hg diff' and 'hg diff -r.' behave still
identically (except for the warning of course).
Added a test for log -r. with one and two parents.
#!/bin/sh
hg init a
cd a
echo bar > foo
hg add foo
hg ci -m 'add foo' -d '1000000 0'
echo foobar > foo
hg ci -m 'change foo' -d '1000001 0'
echo 'quiet:'
hg --quiet diff -r 0 -r 1
echo
echo 'normal:'
hg diff -r 0 -r 1
echo
echo 'verbose:'
hg --verbose diff -r 0 -r 1
echo
echo 'debug:'
hg --debug diff -r 0 -r 1
echo