Use 'unsigned short' for mode, like diff_filespec does
struct diff_filespec defines mode to be an 'unsigned short'. Several
other places in the API which we'd like to interact with using a
diff_filespec used a plain unsigned (or unsigned int). This caused
problems when taking addresses, so switch to unsigned short.
Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>