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 test
cd test
mkdir da
echo foo > da/foo
echo foo > foo
hg ci -Ambase -d '0 0'
hg serve -p 20060 -d --pid-file=hg.pid
echo % manifest
("$TESTDIR/get-with-headers.py" localhost:20060 '/file/tip/?style=raw')
("$TESTDIR/get-with-headers.py" localhost:20060 '/file/tip/da?style=raw')
kill `cat hg.pid`