size_t is bigger than int on most 64-bit machines, so cast
size_t to long when passing them to printf-like functions.

Ideally we'd use %z, but many compilers don't support it.

git-svn-id: https://svn.musicpd.org/mpd/trunk@4656 09075e82-0dd4-0310-85a5-a0d7c8717e4f