adding [minimal] symlink support

[Bryan O'Sullivan]

On Tue, 2006-07-11 at 17:56 -0500, Matt Mackall wrote:

> I don't think I've got time to delve into coding this right now,
> actually.

Well, the reason that I brought up this as being the right time to think
about symlinks is that the merge code will need to be symlink-aware.

Right now, we handle one class of not-quite-content merge conflict: I
modify a file, you delete it, we merge.

However, there are a few other possible merge cases:

I have a file, you have a directory with the same name.  We fall over on
this right now.

I have a file, you have a symlink with the same name.  Of course, we
don't handle symlinks, but this needs handling too.

There are a few other variations (I have a symlink, you delete it; I
have a directory full of files, I add one, you rename the directory)
also worth tossing into the mix.

	<b