RT2308: Add extern "C" { ... } wrapper

Add the wrapper to all public header files (Configure
generates one).  Don't bother for those that are just
lists of #define's that do renaming.

Reviewed-by: Tim Hudson <tjh@openssl.org>
Merge branch 'master' of git.openssl.org:openssl

Gah, I hate when I forget to pull before merging.

Reviewed-by: rsalz