Fix more gcc format warnings:

block/block_compact.c:193:119: error: format specifies type 'uintmax_t' (aka 'unsigned long') but the argument has type 'long long' [-Werror,-Wformat]
block/block_compact.c:202:124: error: format specifies type 'intmax_t' (aka 'long') but the argument has type 'long long' [-Werror,-Wformat]
Fix yet more warnings from gcc 4.6:

block/block_compact.c:193:165: error: conversion to 'long unsigned int' from 'off_t' may change the sign of the result [-Werror=sign-conversion]
block/block_compact.c:203:170: error: conversion to 'long unsigned int' from 'off_t' may change the sign of the result [-Werror=sign-conversion]