isnull.c (uuid_is_null), pack.c (uuid_pack),
parse.c (uuid_parse), unpack.c (uuid_unpack),
unparse.c (uuid_unparse), uuid.h, uuidP.h,
uuid_time.c (uuid_time, uuid_type, uuid_variant):
Use const for pointer variables that we don't modify. Add
the appropriate ifdef's in uuid.h to make it be C++ friendly.
uuid_time.c (main), tst_uuid.c (main): Fix gcc -Wall complaints.
copy.c (uuid_copy): Change arguments to make it clear which argument
is the source and which is the destination.
gen_uuid.c (get_random_fd): Use gettimeofday to seed the PRNG, so we
can take advantage of tv_usec to do (slightly) better at seeding it.