This is perhaps not a question unique to Mercurial, but that's the SCM that I've been using most lately.

I work on multiple projects and tend to copy source code for libraries or utilities from a previous project to get a leg up on starting a new project. The problem comes in when I want to merge all the changes I made in my latest project, back into a "master" copy of those shared library files.

Since the files stored in disjoint repositories will have distinct version histories, Mercurial won't be able to perform an intelligent merge if I just copy the files back to the master repo (or even between two independent projects).

I'm looking for an easy way to preserve the change history so I can merge library files back to the master with a minimum of external record keeping (which is one of the reasons I'm using SVN less as merges require remembering when copies were made across branches).

Perhaps I need to do a bit more up-front organization of my repository to prepare for a future merge back to a common master.