Platform.h issue affecting curve functionality

The curve functionality under the HAVE_LIBSODIUM ifdef's is not compiling in even though I have libsodium and HAVE_LIBSODIUM is properly set in src/platform.h after running configure. I think some recent platform.h changes may have caused this. By including platform.h in zauth.c and zsockopt.c the HAVE_LIBSODIUM evaluation occurs properly. Not sure if this is the right fix though, perhaps czmq.h should include it.

Also includes a trivial fix to Makefile.am to stop an error being reported during autogen.sh run.