Support for packed repeated fields

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It would be useful to be able to atleast decode packed repeated fields.

repeated int32 field = 1 [packed = true];

To be compatible with protobuf-2.4, decoders should understand packed repeated 
fields on input. This should be recognized based on wire type, regardless 
whether packed = true is defined in .proto or not.

(This problem is not so important to me personally, I just ran into it when 
benchmarking nanopb vs. protobuf-embedded-c and thought I would report it.)

Original issue reported on code.google.com by Petteri.Aimonen on 3 Feb 2013 at 4:38