--first-parent plus path limiting

While trying to find out when builtin-fetch.c was merged into master, I
noticed that this:

$ git log --first-parent --pretty=oneline -- builtin-fetch.c

lists b888d61c (Make fetch a builtin), which I did not expect. This one
doesn't list it, as expected:

$ git log --first-parent --pretty=oneline

-- Hannes