Rename SecurityTokenDecoder to SecurityTokenCodec

The class is named inappropriately, as it does even do any decoding. It is renamed to codec to capture both encoding/decoding work for gadget security tokens.

[zhoresh, 2010-07-22 00:12:15]

LGTM

Please also update the UPGRADING file and explain the rename since we might
break anyone that derive from the class.

Paul, is there a reason we should not rename it at this point of time?
if not I will submit.

[Paul Lindner, 2010-07-22 00:20:27]

fine with me.  I was just being careful to not cause merge issues by renaming a
bunch of things.

[mhermanto, 2010-07-22 00:36:19]

Include UPGRADING

[mhermanto, 2010-07-22 00:37:51]

On 2010/07/22 00:12:15, zhoresh wrote:
> LGTM
> 
> Please also update the UPGRADING file and explain the rename since we might
> break anyone that derive from the class.
> 

Done. Re-uploaded patch. All tests passed.

> Paul, is there a reason we should not rename it at this point of time?
> if not I will submit.

[zhoresh, 2010-07-22 02:50:01]

Thanks Paul. I was thinking to reuse the old names and create simple derived
classes/interface to make it backward compatible. But I think it won't work due
to the interface.

Submitted r966481