Deprecate some C++ extensions

[Nathan Sidwell]

This patch deprecates 2 sets of extensions

1)  'T v (init) __attribute__ ((ignored))'
That attribute placement has had no effect since the new parser (2002, I 
think gcc 3.3).  Now we're more noisy about it.

2) anonymous struct or union members could be things other than public 
non-static data members.  Now we're noisier about that too.

I updated the 'Deprecated Features' piece of the documentation, it was 
mentioning some now-removed items as merely deprecated.  It occurs to me 
we should probably just merge the 'Backwards Compatibility' section into 
'Deprecated Features'.  Perhaps add a 'Removed Features' section too? 
Sandra, WDYT?

nathan
-- 
Nathan Sidwell
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