there's not much point to having the "private" definitions split out
into a separate header file. they're still in the namespace and there's
nothing that can be done to prevent "unauthorized" uses. just integrate
the definitions into the main header file but put them in the bottom and
note that they're "private".
this makes it very slightly easier to copy the protobuf-c support
library into another project wholesale, since one less file is required.
for some reason, "make distcheck" fails when the build is configured
with --disable-protoc. i haven't been able to track down the root cause
(it appears the build is trying to generate the generated pb-c files for
the test cases, but the test cases should be disabled when
--disable-protoc is specified). so, remove the --disable-protoc option.
libprotobuf-c should always be tested as part of a build, and this can't
be done unless protoc-c is built. this also reduces the number of build
combinations that need to be tested.
