diff: use the word "path" instead of "name" for blobs

diff: use the word "path" instead of "name" for blobs

The stuff_change() function makes diff_filespecs out of
blobs. The term we generally use for filespecs is "path",
not "name", so let's be consistent here.  That will make
things less confusing when the next patch starts caring
about the path/name distinction inside the pending object
array.

Signed-off-by: Jeff King <redacted>
Signed-off-by: Junio C Hamano <redacted>