Remove useless uses of cat, and replace with filename arguments

Remove useless uses of cat, and replace with filename arguments

Replace uses of cat that do nothing but writing the contents of
a single file to another command via pipe.

[jc: Original patch from Josh was somewhat buggy and rewrote
"cat $file | wc -l" to "wc -l $file", but this one should be Ok.]

Signed-off-by: Junio C Hamano <gitster@pobox.com>