Merge algorithms

[Andrew Bennetts]

Eli Zaretskii wrote:
[...]
> > IIRC, the filename is relative to the root of the tree, so "ChangeLog" will not
> > match "src/ChangeLog".  If you need a more flexible policy let me know and I'll
> > figure out how to adjust the plugin.
> 
> I would like ChangeLog files to in any subdirectory of the root to use
> this plugin.

Ok, I've pushed a small hack to the plugin to make it do that.  Separately I'll
look at improving the helpers in bzrlib to make it easier for plugins to support
arbitrary policies here (matching full paths, or matching base names, or
matching globs, or $arbitrary_function...).

I've also tweaked the plugin help to hopefully be a bit clearer about how to
configure it in branch.conf vs. locations.conf.

Thanks for the feedback so far!

-Andrew.