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
cp $TESTDIR/binfile.bin .
hg add binfile.bin
hg ci -m 'add binfile.bin' -d '0 0'
echo >> binfile.bin
hg ci -m 'change binfile.bin' -d '0 0'
hg revert -r 0 binfile.bin
hg ci -m 'revert binfile.bin' -d '0 0'
echo % diff -r 0 -r 1
hg diff --nodates -r 0 -r 1
echo % diff -r 0 -r 2
hg diff --nodates -r 0 -r 2
echo % diff --git -r 0 -r 1
hg diff --git -r 0 -r 1
echo % diff --git -r 0 -r 2
hg diff --git -r 0 -r 2