pg_backup_tar.c seems anerror by win32

Hi Bruce-san.

Yesterday patch was inadequate....

pg_backup_tar.c: In function `tarOpen':
pg_backup_tar.c:379: `S_IREAD' undeclared (first use in this function)
pg_backup_tar.c:379: (Each undeclared identifier is reported only once
pg_backup_tar.c:379: for each function it appears in.)
pg_backup_tar.c:379: `S_IWRITE' undeclared (first use in this function)
pg_backup_tar.c: In function `_tarAddFile':
pg_backup_tar.c:1051: warning: comparison is always false due to limited range of data type
make[3]: *** [pg_backup_tar.o] Error 1
make[2]: *** [all] Error 2
make[1]: *** [all] Error 2
make: *** [all] Error 2

This patch helps this.
Thanks.

Regards,
Hiroshi Saito