Fix exp in non-default rounding modes (bug 3976)

[Andreas Jaeger]

On 03/02/2012 02:41 PM, Joseph S. Myers wrote:
> Does anyone have comments on the patch itself
> <http://sourceware.org/ml/libc-alpha/2012-02/msg00748.html>?  I think
> we've sorted out the general principle of making libm functions work in
> all rounding modes - and I'd like to do various followup patches for other
> functions.

The patch seems to be the best way to do it, it's fine. Thanks for 
adding testcases as well!

Andreas