Move tar function headers to pgtar.h

This makes it possible to include them only where they are used, so
we can avoid the conflict of the uid_t and gid_t datatypes that happened
in plperl (since plperl doesn't need the tar functions)

src/bin/pg_dump/pg_backup_tar.c

@@ -30,6 +30,7 @@
 #include "pg_backup_tar.h"
 #include "dumpmem.h"
 #include "dumputils.h"
+#include "pgtar.h"
 
 #include <sys/stat.h>
 #include <ctype.h>