[RFC] use buffered stdio (lightly tested)

[Eric Wong]

> index 70f5b74..2c387c1 100644
> --- a/filter.c
> +++ b/filter.c
> @@ -143,22 +145,22 @@ void cgit_init_filters(void)
>  #endif
>  
>  #ifndef NO_LUA
> -static ssize_t (*libc_write)(int fd, const void *buf, size_t count);
> +static ssize_t (*libc_fwrite)(const void *buf, size_t size, size_t n, FILE *);

Oops, that should be size_t:

  static size_t (*libc_fwrite)(const void *buf, size_t size, size_t n, FILE *);

I also think we need to keep hooking write(2) in addition to
fwrite(3), since (I think) the Lua script may call write(2)
outside of the API we provide it.