Runtime: Fix BIT_MIXED after renumbering of PIKE_T_*.

Fixes fatal "Type field out of order" for arrays containing types.
decode_value: Fix handling of inherits.

Use program.c:lower_inherit() in decode_value(). The new
parent flags handling in low_inherit() isn't safe to use
from decode_value(), since the program_state stack isn't
necessarily the same as when the encoded program was
initially compiled.

Fixes various dumping errors.