RelNotes: spelling & grammar tweaks

Signed-off-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git 2.2

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff_populate_filespec: add a PEEK option

This lets callers peek only at the first few kilobytes of
the buffer, which we can then sometimes use to avoid loading
large blobs.