[sv-bc] Updated proposal for `keywords compatibility directive

I have made the amendments to the proposal for SV errata 328, on adding a
`keywords compatibility directive, per the decisions approved in today's
SV-BC meeting.

The amended proposal is attached. I do not know the procedure for uploading
this to the errata data base, so someone will have to do this for me.

Stu
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Stuart Sutherland
stuart@sutherland-hdl.com
+1-503-692-0898