Fix some warnings to allow -Werror

The type used to declare the st_size field of a 'struct stat' can
be a 32- or 64-bit sized type, which can vary from one platform to
another, or even from one compilation to another.  In particular,
on linux, if you include the following define:

    #define _FILE_OFFSET_BITS 64

prior to including certain system header files, then the type used
for the st_size field will be __off64_t, otherwise it will be an
__off_t.  Note that the above define is included at the top of
git-compat-util.h.

In cache.c, the "%zd" format specifier expects a "signed size_t",
another type which can vary, when an __off64_t or a __off_t is
provided.  To supress the warning, use the PRIuMAX format specifier
and cast the st_size field to uintmax_t.  This should work an any
platform for which git currently compiles.

In ui-plain.c, the size parameter of sha1_object_info() and
read_sha1_file() is defined to be "unsigned long *" not "size_t *".
So, to supress the warning, simply declare size with the correct type.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

ui-plain.c

@@ -18,7 +18,7 @@ static void print_object(const unsigned char *sha1, const char *path)
 {
 	enum object_type type;
 	char *buf;
-	size_t size;
+	unsigned long size;
 
 	type = sha1_object_info(sha1, &size);
 	if (type == OBJ_BAD) {