add -p: fix counting when splitting and coalescing

add -p: fix counting when splitting and coalescing

When a file has no trailing new line at the end diff records this by
appending "\ No newline at end of file" below the last line of the
file. This line should not be counted in the hunk header. Fix the
splitting and coalescing code to count files without a trailing new line
properly and change one of the tests to test splitting without a
trailing new line.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>