Fix diagnostic decode_value
Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=6513
Reported by Martin Stjernholm email@example.com
For debugging it is sometimes necessary to be able to decode data structures containing programs without a correct resolver. This is currently enabled by the ENCODE_DEBUG define in encode.c, and then passing a hidden third argument to decode_value. It should be available in normal pike builds, preferably through a separate debug_decode_value function.
This does not mean that the other debug aspects of ENCODE_DEBUG, i.e. all the stderr logging, should be available.