[v3] new staging headers

[Gabriel Dos Reis]

Phil Edwards <pedwards@disaster.jaj.com> writes:

| One additional note:  Gaby, the change of yours from three days ago regarding
| expf and atan2f didn't get run through autoheader to rebuild config.h.in
| and the two HAVE_ symbols.

Hmm, I want configure to continue to test for the existence of those
symbols and define the appropriate macros. 

-- Gaby