Update NEWS with new MPI-3 features and a note about the new ROMIO
version.

cmr=v1.7.4:reviewer=rhc
Remove CFLAGS setting that was really only intended for the v1.6
branch (it's not necessary on trunk/v1.7 because they require C99,
which allows variadic macros).

Also fix another compiler warning (using %p to print a (void*)).

Submitted by Jeff, reviewed by Dave.

cmr=v1.7.4:reviewer=ompi-rm1.7:subject=two usnic BTL fixes
Convert debug output to opal_output_verbose

Thanks to Tetsuya Mishima for reporting it

cmr=v1.7.4:reviewer=jsquyres
Silence warnings that are no longer valid

Refs #3992