windows compile warnings

Here are a few compile warnings I am seeing on Windows. I will try to 
look at some in due course, but I am out of action for at least 2 days, 
so if anyone wants to jump on them please do.

open.c:55: warning: no previous prototype for `win32_open'
dynloader.c:7: warning: no previous prototype for `dlerror'
dynloader.c:13: warning: no previous prototype for `dlclose'
dynloader.c:19: warning: no previous prototype for `dlsym'
dynloader.c:25: warning: no previous prototype for `dlopen'
pgarch.c:349: warning: implicit declaration of function `sleep'
open.c:55: warning: no previous prototype for `win32_open'
pg_backup_tar.c:1022: warning: comparison is always false due to limited 
range of data type
pg_resetxlog.c:104: warning: implicit declaration of function `getopt'

cheers

andrew