patchdiffcore.h: be explicit about the signedness of is_binary

> Bitfields need to specify their signedness explicitly or the compiler is
> free to default as it sees fit.  With compilers that default 'unsigned'
> (SUNWspro 12 seems to do this) the tri-state nature of is_binary
> vanishes and all files are treated as binary.
> 
> Signed-off-by: Richard Lowe <richlowe@richlowe.net>

> Bitfields need to specify their signedness explicitly or the compiler is
> free to default as it sees fit.  With compilers that default 'unsigned'
> (SUNWspro 12 seems to do this) the tri-state nature of is_binary
> vanishes and all files are treated as binary.
>
> Signed-off-by: Richard Lowe <richlowe@richlowe.net>
> ---

>  diffcore.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/diffcore.h b/diffcore.h
> index 79de8cf..7c6f391 100644
> --- a/diffcore.h
> +++ b/diffcore.h
> @@ -46,7 +46,7 @@ struct diff_filespec {
>  	unsigned is_stdin : 1;
>  	unsigned has_more_entries : 1; /* only appear in combined diff */
>  	/* data should be considered "binary"; -1 means "don't know yet" */
> -	int is_binary : 2;
> +	signed int is_binary : 2;
>  	struct userdiff_driver *driver;
>  };