"ignoring copy" message should be more informative

[Daniel Clemente]

This testcase generates an "ignoring copy" message because a file was copied & added and the original one was changed & added afterwards, all before doing commit.

cd /tmp; rm -rf tres3; mkdir tres3; cd tres3; git init; echo hola>uno; git add uno; git commit -m "fichero normal" ; cp uno copiado; git add uno copiado; echo hola2>uno; git add uno; git commit -a -m "modificación y copia"; git fast-export -M -C --all >expo; mkdir enbzr; cd enbzr; bzr init; bzr fast-import ../expo

You get this output:

WARNING: ignoring copy of "uno" to "copiado" - source does not exist (:4)
18:11:48 Updating branch information ...
  branch enbzr now has 2 revisions and 0 tags
18:11:48 Imported 2 revisions, updating 1 branch and 0 trees in 0:00:00
…

  Only after creating that test case can I understand the message. But for a new user who imports a big branch, more information is needed. Concretely: why this can usually happen (so that you may fix it if you want), and what will Bazaar do (will the file be added? will it simply be suboptimal but still completely functional? will it be missing?).
  I know you can usually ignore warnings, but a 1-time conversion of a large branch is an important process on which depends the integrity and other future problems, so users may want to understand it completely; that's at least my case.