configure.ac: add --enable-compat
configure.ac: add --enable-compat

Enable the API compatibility layer that supports wraps the new API in old API.
Its use is meant only for easing transistion to the new API and will remain exactly
one release. It is scheduled to be removed in version 2.1.

mwgoldsmith/dvbpsi,paraeco/libdvbpsi,paraeco/libdvbpsi,paraeco/libdvbpsi,mwgoldsmith/dvbpsi,paraeco/libdvbpsi,mwgoldsmith/dvbpsi,mwgoldsmith/dvbpsi