git filter-branch '--subdirectory-filter' preserving '--no-ff' merges.

(update2, 3/6/2013)

Well, in fact, the name is a bit misleading, because '--subdirectory-filter'
does not preserve merge commits created after fast-forward merge (with
'--no-ff' option). I think, this is because such commits are empty and do not
change any files in subdirectory (so, this is not a bug).

Anyway, i want to split subdirectory into separate project, preserving --no-ff
merge commits.

Strange behavior of git blame '-C' option.

(update1)
'git blame' 's option '-C' works strangely to me, and i'm neither able to find
anything relevent in manpage nor somewhere else.  So, here is just test
results and my speculations, which may be (completely) wrong.