Treat D keywords as identifiers in certain postfix expressions. This allows
one to, for example, access the "provider" field of a struct g_consumer,
even though "provider" is a D keyword.

PR:		169657
MFC after:	2 months
Discussed with:	Bryan Cantrill
Sponsored by:	EMC / Isilon Storage Division


git-svn-id: svn+ssh://svn.freebsd.org/base/head@272671 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f