Coordinating libffi upgrade

[Anthony Green]

Several months ago I attempted to upgrade libffi 3.0.10 to 3.0.11.  The change was
reverted because the soname change in this version of the library broke the build
environment.  I would still like to get 3.0.11 in Fedora.  I don't anticipate any
future ABI-breaking changes, and 3.0.12 will include additional ports like Aarch64, which
is likely of interest to some Fedora developers.  How do we coordinate a rebuild for
dependent packages?  Also, I assume this will have to wait 'til F18 is out (fine by
me), but I'd like to deal with it early in the F19 cycle.

Thanks,

Anthony Green